OBJECTIVE: To study the association between BMI and lifestyle factors such as alcohol consumption, smoking habits, education level and marital status in a Spanish graduate population. METHOD: Cross-sectional analysis of 8,706 participants (3,643 men and 5,063 women) from the Seguimiento Universidad de Navarra (SUN) Study, an ongoing dynamic cohort study in Spain. Data on body weight, height and sociodemographic characteristics, and lifestyle habits were collected with self-administered validated questionnaires. RESULTS: Among older participants (above sex-specific median age), educational level was a factor independently associated with BMI. University graduates with a lower educational level (3-year college degree or 5-year university degree) had a significantly higher BMI than those with doctorate which requires, at least, 8 years of university studies in Spain. Mean BMI was significantly higher among past smokers than among never smokers. Alcohol consumption, marital and smoking status were associated with BMI only among men. CONCLUSION: In a study whose members were all university graduates, several factors were independently associated with a higher BMI, such as less years of higher education, past smoking, marital status and higher alcohol consumption.