Purpose: Parastomal hernia continues to be an important clinical problem with a reported incidence of up to 50 percent. In studies using computerized tomography in selected cases for detection of parastomal hernia, physical examination alone was underestimating the true incidence. Also after closure of the enterostomy, the ostomy site could still be a potential area of herniation. In this study in addition to physical examination, we used computerized tomography to determine the true incidence of parastomal hernia and ostomy closure site hernias. Methods: We examined patients with enterostomies and with closed enterostomy sites both with physical examination and computerized tomography for the detection of hernias, hernia content, and relation to rectus muscles. Risk factors for hernia formation, such as age, gender, body mass index, associated medical problems, and surgical site infections, were determined. Results: Evaluation of 23 patients with ostomies resulted in 52 percent incidence of parastomal hernia, whereas the addition of tomography examination gave a corrected incidence of 78 percent. In a second subset of 23 patients with closed ostomies, although 26 percent of the patients were found to have ostomy site hernias with physical examination alone, this incidence increased to 48 percent when combined with computerized tomography. The potential risk factors for hernia formation, such as body mass index, surgical site infection, and ostomy site whether pararectus or transrectus, were not proven to have a significant role in this study. Conclusions: Parastomal hernia and closed ostomy site incisional hernias have a high incidence, and computerized tomography has been shown to be a valuable diagnostic tool.