STUDY DESIGN: Cross-sectional study. Women giving birth at one of two hospitals of northern Sweden from 1 January 2002 until 30 April 2002 were invited to fill in a questionnaire on their obstetric and gynecological history, actual pregnancy, and delivery. OBJECTIVE: The aim of this study was to investigate prevalence and risk factors for low back pain and pelvic pain (LBPP) during pregnancy. SUMMARY OF BACKGROUND DATA: Although low back pain and pelvic pain during pregnancy is a most common complication of pregnancy, its etiology is unknown and the pathophysiology is poorly understood. METHODS: The sample was analyzed by calculating the prevalence of LBPP during pregnancy. Univariate and multivariate logistic regression was performed to calculate odds ratio (OR) and its 95% confidence intervals (CI) where applicable. Parametric and nonparametric testing was used to establish differences between groups. RESULTS: The response rate was 83.2% (N = 891). The prevalence of LBPP during pregnancy was 72%. Most cases reported both anterior and posterior pain. Increasing parity, history of hypermobility, and reported periods of amenorrhea were risk factors for LBPP. Women with LBPP had significantly higher prepregnancy weight, end-pregnancy weight, and prepregnancy and end-pregnancy body mass index. Age at menarche and use of oral contraceptives were not associated with LBPP. Nonrespondents were of the same age and parity as respondents. CONCLUSIONS: A majority of pregnant women report LBPP. Parity, LBPP during a previous pregnancy, body mass index, a history of hypermobility, and amenorrhea are factors influencing the risk of developing LBPP during pregnancy.