Background and Objectives: The number of breast cancer in women has increased dramatically in Tunisia. The cause is perceived to stem from adaptation to a westernized life style which increases body mass index (BMI). This study aimed to investigate the association between BMI and breast cancer among Tunisian women. noneDesign and Setting: Hospital-based case control study of breast cancer patients seen between November 2006 and April 2009 at the University College Hospital Farhat Hached in Sousse, Tunisia. Patients and Methods: Standardized questionnaires concerning BMI and other anthropometric data were completed on 400 breast cancer cases and 400 controls. The controls were frequency-matched to the cases by age. Results: BMI at diagnosis was positively correlated with the risk of breast cancer among postmenopausal women (P