Round window fistula as a cause of sudden hearing loss was diagnosed in five people. It was associated with a sudden change in middle ear pressure in three, with heavy lifing in one, and was probably caused by a significant blast exposure in the other. The clinical features of the condition are varied, with hearing loss and tinnitus being the only constant findings in our patients. One case demonstrates, perhaps for the first time, the association of an abnormally mobile portion of the round window membrane with vertigo and nystagmus. Suggestions on identification and management of round window fistula are made.