The first episode filmed after Jeremy Brett began treatment for bipolar disorder.
The film was broadcast 100 years after the novel's setting of 1887.
In the original story, Dr Watson becomes engaged to marry Mary Morstan. In this adaptation he is clearly taken with her but the writers left it at that.
Small identifies the penal colony as being on "Blair Island." In fact the location was in Port Blair, on Chatham Island. The British operated a naval base and penal colony there from 1789-91. The colony was moved to Port Cornwallis on Great Andaman, and abandoned in 1796. The colony was then re-established at Port Blair in 1858, to handle prisoners convicted of offenses during the Indian Mutiny of 1857. Port Blair is now the capital of the Andaman and Nicobar Islands, a "union territory" of India.
The producers used The Walker Art Gallery in Liverpool as the location for the Lyceum Theatre.