OBJECTIVE To determine the genetic and environmental influence on the liability for stress urinary incontinence and pelvic organ prolapse surgery. METHODS We used the Swedish Twin Registry to identify all same-sex female twin pairs with known zygosity born from 1926 to 1958. Occurrence of stress urinary incontinence and pelvic organ prolapse surgery was determined by cross-linkage to the Swedish Inpatient Registry. By comparing mono- and dizygotic female twins, we determined twin similarity and the relative proportions of phenotypic variance resulting from genetic and environmental factors. Using statistical modelling, the liability for pelvic floor surgery explained by heritability versus shared and non-shared environmental effects was estimated. RESULTS We identified 3376 complete monozygotic and 5067 dizygotic same-sex female twin pairs. There was greater twin similarity among monozygotic compared with dizygotic twins, which indicates the influence of a genetic component to the aetiology of both stress urinary incontinence and pelvic organ prolapse surgery. For both disorders, genetic and non-shared environmental factors equally contributed about 40% of the variation in liability. Shared environment accounted for approximately one fifth of the total variance for the two disorders. CONCLUSIONS Genetic effects contribute to the occurrence of both stress urinary incontinence and pelvic organ prolapse, but the influence of environmental factors is substantial. Significant environmental effects suggest that the liability for benign pelvic floor surgery is amenable to intervention.