Background: One of the United Nations' Millennium Development Goals for 2015 is to reduce the maternal mortality ratio by three fourths. Ninety-nine percent of maternal deaths occur in developing countries, and the World Health Organization encourages investigations in these settings to determine the risk factors of maternal deaths. Our aim was to identify these risk factors in a hospital-based study in Mexico. Methods: The study was conducted at the Hospital of Obstetrics and Gynecology at the Mexican Institute of Social Security in Leon, Guanajuato, Mexico, from January 1, 1992, to March 31, 2004. Women were divided into groups of 110 individuals who had died during pregnancy, delivery, or postpartum, and 440 women who survived the postpartum period. We used a logistic regression analysis to find the significant risk factors for maternal deaths. Odds ratios with 95% t confidence intervals were estimated. Results: The maternal mortality ratio was 47.3 per 100,000 live births. The main causes of death were hemorrhage (30.9%), preeclampsia/eclampsia (28.2%), and septic shock (10.9%). Six factors were significantly associated with maternal death: age (OR = 1.09, 95% CI = 1.00-1.18), marital status (OR = 16.2, 95% CI = 1.3-196.1), number of antenatal visits (OR = 1.3, 95% CI = 1.0-1.6), preexisting medical conditions (OR = 23.3, 95% CI = 6.6-81.6), obstetric complications in previous pregnancies (OR = 28.3, 95% CI = 4.9-163.0), and mode of delivery (OR = 1.6, 95% CI = 1.0-2.4). Conclusions: Socioeconomic, medical, and obstetric risk factors are associated with maternal deaths in Mexico. (BIRTH 34:1 March 2007)