Oral manifestations were studied in 87 HIV-positive Thai adults (study 1), 45 HIV-positive children (study 2) and 101 HIV-positive (study 3). In study 1, 48% of patients had oral lesions; 23% had one and 13.8% two oral manifestations. Oral pseudomembranous candidiasis was found in 10.3%, erythematous candidiasis in 6.9%, and hairy leukoplakia (HL) in 11.5% of the patients. In study 2, 24.4% of children revealed one, 17.8% two and 6.6% three oral lesions; erythematous candidiasis was seen in 17.8%, and HL in 6.7% of the children. Fifteen patients (33.3%) received antiretroviral therapy. In study 3, pseudomembranous candidiasis was found in 52.5%, HL in 35.6% and necrotizing gingivo-periodontitis in 27.7%. Only 10% of patients were without oral lesions. The present three studies among HIV-infected Thai and Cambodians indicated a high prevalence of oral lesions, particularly variants of oral candidiasis such as pseudomembranous and erythematous candidiasis. Also, oral HL was a common finding, more so in patients with AIDS-associated diseases as represented by patients of study 3. Oral candidiasis and oral HL also seem to be quite prevalent in pediatric HIV-infected patients. In the absence of parameters indicating the degree of immunosuppression (CD4+ cell counts and viral load) these oral lesions may be considered strong indicators of HIV-associated immunodeficiency.