The purpose of this study is to evaluate the prevalence of overweight and obesity and associated factors among Mexican-American adolescents, because obesity is more common among this ethnic group. The National Health and Nutrition Examination Survey 1999-2002 data were analyzed for Mexican-American adolescents aged 12 to 19 years (n=4,109). Weight status was determined by sex-specific body mass index for age, and evaluated in relationship to demographic characteristics, participation in physical activities, dietary intake, and general health status. Overall, 40.9% of the adolescents were overweight and 22.9% were obese. Males had a higher prevalence of overweight and obesity than females. Factors associated with overweight included being from a low-income family, perceiving oneself as less physically active compared to others of the same age, having a history of asthma, and having considerably higher blood pressure. However, overweight adolescents reported a substantially lower intake for calories and all evaluated nutrients compared to nonoverweight adolescents. It is important to be aware of the high prevalence of overweight among Mexican-American adolescents, as chronic diseases such as hypertension start early among overweight adolescents. Culturally appropriate programs should be created for this ethnic group aimed at obesity prevention and weight management, including nutrition education and individual dietary counseling, with the ultimate goal of lifelong healthful eating habits.