The purpose of this study was to demonstrate the role of high-resolution real-time sonography in the diagnosis of spigelian hernias. The sonographic findings in three patients, two of whom had surgical confirmation, are presented. We also discuss and demonstrate the anatomic and pathologic factors that predispose to these hernias. In all three cases, real-time high-resolution sonography was very helpful in providing detailed images of the abdominal wall defect, the hernial sac and contents, and the relationship of the contents to the spigelian fascia and the rectus, external oblique, and internal oblique muscles. The role of the Valsalva and other provocative maneuvers in demonstrating the "in and out" sliding movement of the contents of the hernia also is discussed. Although the number of cases in our study is small, we think that this modality may be the most effective means for establishing this diagnosis, especially in cases with equivocal clinical findings.