The relationships between asthma in adolescents and various environmental and social exposures needs to be clarified. The aim of this study was to determine the association between family history of allergy, passive or active tobacco smoking, obesity, and asthma in adolescents. A population-based case-control study was carried out. A random sample of 4003 students aged 13 to 18 years old was selected from secondary and preparatory schools in an urban area in northeastern Mexico. Data was gathered in physical examinations and with a questionnaire administered by trained staff. Two study groups were formed: a group of 253 adolescents with asthma and a control group of students without asthma. Variables associated with asthma were family history of allergy (odds ratio [OR], 1.62; 95% confidence interval [CI], 1.28-2.06), passive smoking (OR, 1.53; 95% CI, 1.18-1.99), and obesity (OR, 1.96; 95% CI, 1.45-2.65). Female gender and active smoking were unrelated to asthma. The percentage of obese adolescents was higher in the group of asthmatics (18.2%) than in the control group (12.8%). Family history of allergy, passive tobacco smoking, and obesity seem to be the main risk factors for the development of asthma in adolescents. The relationship of active smoking and asthma requires further study.