A one-year prospective study into the aetiology of corneal ulceration in 103 patients attending Mvumi hospital, Tanzania, showed 25% (95% CL 16.5-33.5%) of ulcers to be associated with the use of traditional eye medicines (TEM) within the previous 7 days. There was no statistically significant difference between TEM users and non-users in terms of sex of the patients, season of presentation or age at presentation. Of 26 corneal ulcers in TEM users, 58% (n = 15) had no other identified cause of ulceration apart from TEM use. Of the remaining 11, eight showed the appearances of HSV keratitis, and three others had bacterial infection, two with Neisseria gonococcus. TEM use was associated with hypopyon at presentation (19.3 vs 2.6% in non-TEM users (P = 0.004)), and there was a trend to more central and dense corneal scarring in the TEM users group (42 vs 23%, P = 0.06). Secondary infection is an important cause of corneal scarring following TEM use, and all patients who have a TEM-associated corneal ulcer should have intensive antimicrobial treatment. TEM use will continue so long as primary eye care continues to be unavailable to the majority of the population of Africa.