Obesity is frequently accompanied by peripheral hyperandrogenism, which may be associated with increased sebum production and the development of severe acne. Body mass index (BMI) is one of the most accurate ways to measure and determine obesity. The aim of the present study was to study the correlation between obesity and the point prevalence and patterns of acne in schoolchildren. A total of 3,274 children (aged 6-11 years) from Magong Township were examined by two board-certified dermatologists. The acne prevalence was 7.3%, with more girls affected than boys (ratio = 1.5). Comedones were more commonly observed than inflammatory acne (10.4% vs. 6.9%). The mean of BMI in non-acne students (18.2 +/- 3.4) was significantly lower than that in acne subjects (19.5 +/- 3.7), without gender difference. Overall schoolchildren with a BMI < 18.5 had less prevalence rate of acne, especially the inflammatory lesions, while those with a BMI-for-age > or = 95% had a significantly higher rate of acne development.