A cross-sectional study carried out among 418 adolescents between ten and 19 years old at a private school in the city of São Paulo in 1998. The objective of the study was to evaluate the proposed thresholds for diagnosing overweight among Brazilian adolescents. The percentage body fat was measured by dual energy X-ray absorptiometry. The cutoff points used for excess body fat were 25% for boys and 30% for girls. The body mass index was classified in accordance with Cole et al and with Conde & Monteiro. The Brazilian reference (Conde & Monteiro) presented higher sensitivity among younger girls (44.2% vs. 32.6%), older girls (18.9% vs. 17%) and older boys (83.3% vs. 50%). The Conde & Monteiro proposal presented higher positive and negative predictive values and provided higher-sensitivity predictions of excess body fat among the study population