One hundred and twenty-five HIV-infected patients, of whom 49 (39%) were at early stages of the infection (CDC-II & III) and 76 (61%) in CDC IV, were prospectively examined. In 100 (80%) one or more oral mucosal lesions were observed; candidiasis (51%) and hairy leukoplakia (43%) were the commonest. Erythematous candidiasis was more often seen (35%) than the pseudomembranous type (16%), and appeared with the higher values at early than later stages. The prevalence of hairy leukoplakia, oral hyperpigmentation and xerostomia were incremented in groups CDC-IV. Pseudomembranous candidiasis and exfoliative cheilitis increased significantly with severity of disease. Our study demonstrates that oral alterations associated to HIV are a frequent finding, both at early (76%) and late (83%) stages of the infection in Mexican patients.