A malodorous, homogeneous, grey, thin and non-purulent discharge, which resembles non-specific vaginitis occurs in 20% of women with an intrauterine contraceptive device (IUCD); four times more common than in non-users. The aim of this investigation was to study the bacteriological aetiology of this IUCD-associated vaginal discharge, and to assess whether the infection was ascendent. No specific microbiological aetiology was found, but the normal, Lactobacillus-dominated microbial vaginal flora was replaced by Gardnerella vaginalis and certain anaerobic species in IUCD-users with the discharge. Clue cells, pepper-salt phenomenon and curved rods and/or fusiform-shaped rods demonstrated by microscopy, were typical of symptomatic patients. The endometrium and the IUCD were infected with these species in the symptomatic group more often than in IUCD-users who had no symptoms or in the control women who did not use the IUCD.