The dispatcher's voice on the program was that of Shaaron Claridge. Claridge was a real Los Angeles dispatcher. Producer Jack Webb thought that using a real dispatcher for the voice-overs would lend authenticity to the program. He did the same thing for Emergency! (1972), casting a real-life emergency dispatcher to voice the role.

In keeping with the reputation of Jack Webb's series being scrupulously accurate about police procedures, selected episodes of this series were used in police academies as instructional films.

The metallic blue Corvette Kent McCord was shown driving in several episodes was the same make and model car that Martin Milner drove in Route 66 (1960).

The paramedics from Emergency! (1972) sometimes crossed paths with the cops at Rampart Hospital.

The LAPD station building where the show was based was the Rampart Division, northwest of downtown Los Angeles.

In the final episode, Reed received the Medal of Valor for saving Malloy's life.

Martin Milner's daughter, Amy, made a guest appearance playing the daughter of a shopkeeper shot during a robbery. Look for her as Debbie McMahon in season seven, episode fourteen, "Victim of the Crime".

The "one" in "One Adam 12" stood for the area of the division, in which they were stationed, "Adam" referred to the type of car they drove (a two-man patrol car) and "12" was for the area they patrolled. However, "one" was the code for Central Division (downtown). Since the unit was shown working in Rampart Division, the actual call sign should have been "Two Adam 12"

Fresh out of the academy, Probationary Officer Jim Reed is paired with veteran Officer Pete Malloy. However, Kent McCord had already appeared as LAPD Officer Jim Reed in several Dragnet 1967 (1967) episodes nearly a year before this show debuted.

Malloy's badge number was 744 and Reed's was 2430. Badges are reissued once an officer retires, so the permanent numbers are "Serial Numbers". Reed's serial number was 13985, which would coincide with an Academy class from 1968, the year Reed was supposed to have joined the LAPD. Malloy's serial number was 10743.

In the early seasons, the officers wore the eight-point hats, and the buttons on their shirt pockets, and epaulets on the shoulders, were brass, and the jackets were of the wool Melton type. When Edward M. Davis became LAPD Chief, he did away with these items, and went with a round hat, antique silver buttons, and the Eisenhower type of jackets, which was reflected in later seasons.

During the period that this show was filmed, the state of California-issued six digit vehicle license plates in the letter and number format (ABC123). The final letter was never I, O, or Q, so that they would not be confused as numbers. The non-police vehicles on the show usually have the letter "I" as the final letter, indicating that it was a movie or television prop plate.

The patrol cars in the series were not real LAPD cruisers, but were purchased by Universal from Chrysler Corporation and American Motors, and outfitted by the Prop Department to LAPD cruiser specifications. In order, the cars were: 1: 1967 Plymouth Belvedere 383 V8 ("pilot" only); 2: 1968 Plymouth Belvedere 383 V8 (season one); 3: 1969 Plymouth Belvedere 383 V8 (seasons two and three); 4: 1971 Plymouth Satellite 383 V8 (season four); 5: 1972 AMC Matador 401 V8 (starting in season five).

The car used for Reed and Malloy's close-ups was towed by camera car. The car's windshield showed reflections of the camera and crew, so the car's windshield was removed. However, this led to the wind blowing Reed and Malloy's hair, so a shield was created to enclose the camera and front of the car.

According to the LAPD training officers doing the audio commentary on the season two DVDs, the little medallions that Reed and Malloy wore on their uniforms signified their shooting abilities. In the case of Malloy, who had a gold medallion with two bars, he was rated as an distinguished expert shot, while Reed, who had a silver medallion with one bar, was a sharpshooter. The commenting officers also explain that police officers are required to be tested on their shooting skills every two years in the LAPD.

Martin Milner's youngest son, Andrew, drove a mini bike as Johnny Whitaker's stunt driver in season six, episode eleven, "Northeast Division".

Kristin Harmon, who played Jim Reed's wife Jean during the final season, was married to Ricky Nelson, who also happened to be one of Kent McCord's best friends. She was billed as Kristin Nelson.

While the series used "1 Adam 12", LAPD units used odd numbers for beats, so they would have been "1 Adam 11" or 1 Adam 13". The only even numbers were used by the supervisors (Sergeants) and they would have been the numbers 10, 20, et cetera, so "1 Adam 12" would never have been an actual assigned number. But, this point is rendered moot by this show having been fictional.

In the later seasons, Malloy's personal vehicle was a tan AMC Matador coupe. In a few episodes, he complains of it "needing to go into the shop". This issue plays a major part in one episode from the last season.

During scenes where Reed and Malloy received a radio call in the patrol car, real-life LAPD dispatcher Sharon Claaridge would lie on the floor in the back and say her lines, so the timing between the dispatcher and the officers would be perfect. Her actual "dispatches" would be added later in post-production.

Also seen in many episodes was a gold Mustang with a white top.

During the final season, Malloy had a girlfriend named Judy, who was often talked about and appeared in a couple of episodes. She was played by Aneta Corsaut.

During the first couple of seasons, Reed and Malloy had an informant named T.J. (played by Robert Donner) who was a recovering heroin addict.

In the first five or six seasons, Kent McCord wore a wedding ring. In later seasons, he didn't.

A blue Ford Maverick was parked somewhere in almost every episode.

The revolvers carried by Malloy and in later seasons Reed, sport wood grips with finger grooves. These are commercially available from several makers today but in the late 1960s and early 1970s they would have been viewed as somewhat exotic. The grips used on the show were custom made by former LAPD gun range master Earl "Fuzzy" Farrant.

The car number on the patrol car in the early seasons Malloy and Reed drove around in was 817 that later changed to 012.

Officer Malloy's bachelor status was a major plot element, but Martin Milner had actually been married 12 years (with 4 children) when the series began. Kent McCord had been married 7 years (with 1 child; 2 more were born later).

Spoofed in Mad Magazine as "Boredom-12".