The purpose of this study was to determine the pattern of STDs among commercial sex workers (CSWs) in Ibadan, Nigeria. The subjects were 169 CSWs randomly selected from 18 brothels, majority of who were examined and investigated in their rooms. Another 136 women without symptoms who visited the special treatment clinic, University College Hospital, Ibadan were selected as a normal control group. Vaginal candidiasis was the most common STD diagnosed in both CSWs and the control group. The other STDs in their order of frequency were HIV infection 34.3%, non-specific vaginosis 24.9%, trichomoniasis 21.9% and gonorrhoea and "genital ulcers" had an incidence of 16.6% each. Other important conditions were tinea cruris 18.9%, scabies 7.7% genital warts 6.5% and 4.1% of them had syphilis sero-positivity. All the 13 CSWs that had scabies, the 4 (36.4%) with genital warts and the 19 (67.9%) with "genital ulcers" had HIV infection. While there was no significant difference between the CSWs with vaginal candidiasis, gonorrhoea, trichomoniasis and the control group, the HIV positivity was significantly higher (P < 0.001) in CSWs than in the control subjects. These findings suggest that women who exchange sexual services for money can no longer be ignored, and should therefore be identified and made to participate in STD prevention and control programmes.