BACKGROUND Acne is a common disease in adolescents, but there are no epidemiological data for acne in Brazil. OBJECTIVES To estimate the prevalence and degree of acne in adolescents from Sao Paulo and study socio-demographic factors, family history and lifestyle, associated with the disease. METHODS Cross-sectional study with 452 adolescents aged between 10 and 17 (mean=13.3 years), students from elementary and high school, examined by 3 independent evaluators. RESULTS 62.4% were female, 85.8% white and 6.4% were aged 14. The prevalence was 96.0% and increased with age - all students over 14 had acne. The most prevalent form of acne was comedonal (61.1%), followed by mild (30.6%) and moderate (7.6%) papular-pustular, which affected mostly the face (97.5%). About half of the adolescents reported family history for acne in mother or father, and 20.6% reported previous treatment for acne. There was a higher chance of presenting non-comedonal acne with increased age (p<0.001).DISCUSSIONThe prevalence of acne in adolescents varies widely due to the clinical features and diagnostic methods used. Adolescents whose brothers/sisters had acne (OR=1.7-p=0.027) and those over 13 (OR=8.3-p<0.001), were more likely to have non-comedonal acne.CONCLUSION This study showed high prevalence of acne in adolescents from Sao Paulo, predominantly the comedonal form on the face, with a higher chance of presenting non-comedonal acne with increased age.