Smoking among medical students has been found to vary strongly between European countries. Few studies have addressed factors associated with smoking among medical students within countries. In this study, we assessed the association of parental smoking and sociodemographic factors with smoking habits of medical students at the University of Ulm, Germany, Students who entered the 1st, 3rd and 5th year of medical school in fall 1992 were asked to complete a self-administered questionnaire. Questionnaires were returned by 696 (85.2%) of 817 eligible students. Overall, 23.7% of students were current smokers, and 11.9% were former smokers. Smoking habits were related to maternal smoking: Odds ratios for the association of maternal smoking with ever or current smoking of students were 2.11 (95% CI: 1.48-3.03) and 2.01 (95% CI: 1.35-3.01), respectively, after adjustment for potential confounders in multiple logistic regression. In contrast, no association was found between paternal smoking and students' smoking status. Male students were more likely to smoke than female students, and living in a large city during secondary school was also associated with ever smoking. No association was found between students' smoking habits and educational achievement of their mothers and fathers. These results suggest a key role of maternal smoking for smoking among medical students in this society.