PURPOSE: There is little evidence regarding the prevalence or incidence of parastomal hernia, but it is thought to be common. Repair of parastomal hernia can be troublesome, and methods of repair need to be validated based on reduced incidence following surgery. The true rate of parastomal herniation needs to be determined prospectively, and risk factors for developing such hernias need to be more clearly defined. METHODS: To determine prevalence and associated risk factors, prospective data were collected regarding initial stoma surgery, presence of parastomal hernia, and comorbidities. RESULTS: Ninety patients were prospectively audited. For stomas formed at emergency or elective surgery,regardless of surgical indication, the overall rate of parastomal hernia was 33 . Aperture size and patient age were independently predictive of parastomal hernia in multivariate analysis. For every millimeter increase in aperture size, the risk of developing a hernia increased by 10 (odds ratio, 1.10 (CI, 1.03a??1.18); P .005). For every additional year of patient age, the risk of developing a hernia increased by 4 (odds ratio, 1.04 (CI, 1.00 a??1.08); P .04). There was a significantly higher prevalence of hernia following sigmoid colostomy than following ileostomy (45.9 vs. 22 ; P .05). The hernia rate was higher but did not reach statistical significance in patients with disseminated malignancy, body mass index 35 kg/m2, diabetes, prostate hypertrophy, ascites, or chronic constipation. CONCLUSION: This study of carefully and prospectively collected data shows the prevalence of parastomal herniation to be 33 . This rate was higher with larger aperture size and increased age in multivariate analysis.