Background: bronchial asthma is a common chronic respiratory disease affecting adolescents and young adults nationality and worldwide and its prevalence has increased in developed and developing countries over the last three decades. Aim of the Work: to establish the prevalence of bronchial asthma among medical students in Saudi Arabia and the relationship between asthma and some associated risk factors. Patients and Methods: a descriptive cross-sectional study. Data were collected from randomly selected undergraduate medical students of 6 universities, during the academic year 2017-2018. A predesigned questionnaire was disseminated to the targeted population to complete it. Results: the prevalence of physician-diagnosed bronchial asthma in our participants was 19.2%. Males reported insignificant higher prevalence of bronchial asthma compared to females (P= 0.195). Bronchial asthma was significantly associated with skin allergy 32.9% (P= 0.001), allergic rhinitis 61.6% (P=0.001), hay fever 12.3 %( P=0.001) and obesity 28.8% (P0.009). While it was insignificantly associated with smoking (P=0.428), passive smoking (P=0.561), diabetes (P=0.254) and performing muscular exercise (P=0.322). Precipitating factors to bronchospasm was dust in 43.8%, certain foods in 1.4%, hot weather in 2.7% and multiple factors in 52.1%. Herbal treatment was tried in 34.2%; desensitization in 6.8% and 68.5% needed emergency treatment. Response to medical treatment was good in 89.1% of cases. Conclusion: the prevalence of physician-diagnosed bronchial asthma in our participants was 19.2%. Males reported insignificant higher prevalence of bronchial asthma than females.  Bronchial asthma was significantly associated with skin allergy, allergic rhinitis, hay fever and obesity. While it was insignificantly associated with active smoking or passive smoking.