A cross-sectional analysis was conducted in Mexico City from September 1989 to March 1996, to determine the prevalence of HIV-related oral manifestations by gender and route of HIV transmission. The diagnosis of HIV-associated oral lesions was based on preestablished criteria. For the statistical analysis chi-squared and Fisher's exact tests were used where appropriate. Odds ratios were calculated as estimates of the relative risks. Control of confounding factors was performed by logistic regression models. Oral lesions were present in 75% of 436 HIV+ patients. Hairy leukoplakia, erythematous and pseudomembranous candidosis, angular cheilitis and oral ulcers were frequently found. Patients who contracted HIV through blood transfusion were more likely to present erythematous candidosis (P=0.005) than subjects who acquired HIV through sexual transmission. Oral ulcers were seen only in men (P=0.02) and in individuals who contracted HIV through sexual transmission (P=0.02). This study brings valuable data in regard to differences in the type and prevalence of HIV-related oral lesions by gender and the risk categories analysed, particularly blood transfusion.A cross-sectional analysis conducted in Mexico City, Mexico, in 1989-96 investigated the prevalence of HIV-related oral manifestations by gender and route of HIV transmission. The 436 HIV-positive patients enrolled in this study were part of a larger, ongoing study conducted through the Infectious Diseases Clinic in Mexico City. The primary mode of HIV transmission was blood transfusion among female respondents (63%) and sexual activity among male respondents (90%). 71% of subjects had at least 1 (mean, 1.3) HIV-related oral lesion, including hairy leukoplakia, erythematous and pseudomembranous candidosis, angular cheilitis, and oral ulcers. Candidosis, pseudomembranous candidosis, hairy leukoplakia, exfoliative cheilitis, and xerostomia were all significantly associated with a CD4 count under 200 cells/cu. mm and were more prevalent among those with advanced HIV disease. Oral ulcers were present only in men. Women had a higher prevalence than men of hyperpigmentation (10.5% vs. 4%) and xerostomia (7% vs. 2%), but these differences were not significant. Multivariate analysis revealed a significant association between erythematous candidosis and blood transfusion, even after controlling for gender, clinical stage, CD4 count, antiretroviral therapy, smoking history, and xerostomia.