The teardrop shadow of the pelvis is poorly understood and as a result its clinical significance is not appreciated. The structure responsible for this shadow was pinpointed by removing sections from the hemipelvis of an anatomic specimen with an electric saw. This structure is located in the anteroinferior portion of the acetabular fossa at the acetabular notch and consists of cortical and medullary bone contributed primarily from the ischium with a much smaller contribution from the superior pubic ramus. The normal and abnormal appearances of the teardrop shadow of the acetabulum of three patients were demonstrated on both plain radiographs and computed tomographic (CT) scans.