This movie marked the end of Akira Kurosawa's collaboration with Toshirô Mifune. They collaborated together in 16 films.
Akira Kurosawa's desire for authenticity for this film led to having the hospital set thoroughly stocked with expensive medical supplies of the time period the film's set in. The drawers that were never referred to or opened on camera, were nevertheless filled with pills.
Period construction of the hospital went as far as to use the right kind of aged wood that would have been used in the region at the time the film is set, per Akira Kurosawa's request.
Before filming the flashback scene when Sahachi is dying in Red Beard's clinic, Akira Kurosawa played the last movement of Ludwig van Beethoven's Ninth Symphony, instructing the cast that this was how he wanted to audience to feel when watching this scene. It was the first scene being filmed for the movie, and helped set the tone for the rest of the film.
Toshirô Mifune usually appeared in several films a year for Toho, doing many cameos and guest roles. However, he chose not to do any that year as he filmed this movie, allowing himself to be fully immersed in what would be his last film for Akira Kurosawa.
The clinic was built based on the modeling of the Koishikawa Nursing Home, which was built in 1722. Original blueprints for the structure were uncovered and used, as well.
According to the DVD commentary by film scholar Stephen Prince, this is the only Akira Kurosawa film to feature nudity.