OBJECTIVE To investigate the risk factors for pelvic organ prolapse (POP), including physical activity, clinically measured joint mobility and pelvic floor muscle (PFM) function. METHODS One-to-one age- and parity-matched case-control study. METHODS Akershus university hospital and one outpatient physiotherapy clinic in Norway. METHODS Forty-nine women with POP (POP quantification, stage>or=II) and 49 controls (stages 0 and I) were recruited from community gynaecologists and advertisements in newspapers. METHODS Validated questionnaires, interview and clinical examination, including Beighton's scoring system (joint hypermobility) and vaginal pressure transducer measurements (PFM function), were used. Univariate and multivariate conditional logistic regression analyses for one-to-one matched case-control studies were used, and odds ratios with 95% CIs are reported. METHODS Pelvic floor muscle function (strength, endurance and resting pressure), socioeconomic status, body mass index, heavy occupational work, physical activity, family history, obstetric factors and markers of connective tissue weakness (striae, varicose veins, bruising, diastasis recti abdominis, joint hypermobility). RESULTS No significant differences were found between groups with regard to postmenopausal status, current smoking, current low-intensity exercise, type of birth (caesarean, forceps, vacuum), birth weight, presence of striae, diastasis recti abdominis and joint hypermobility. Body mass index (OR 5.0; 95% CI 1.1-23.0), socioeconomic status (OR 10.5; 95% CI 2.2-50.1), heavy occupational work (OR 9.6; 95% CI 1.3-70.3), anal sphincter lacerations (OR 4.5; 95% CI 1.0-20.0), PFM strength (OR 7.5; 95% CI 1.5-36.4) and endurance (OR 11.5; 95% CI 2.0-66.9) were independently related to POP. CONCLUSIONS Body mass index, socioeconomic status, heavy occupational work, anal sphincter lacerations and PFM function were independently associated with POP, whereas joint mobility and physical activity were not.