Ten cases of so-called development defect were detected on panoramic radiograms. One of them was bilocular, two were round, three were ovoid, and four were half-ovoid. Eight were in men and two were in women. These cystlike lesions are sometimes misdiagnosed as epithelium-lined cysts or benign tumors, such as ameloblastoma. For the detection of this kind of defect, panoramic radiography is available, and the lesion is differentiated from many cysts and tumors in the jaws by posteroanterior projection and occlusal films. From the published literature, some tendencies of age distribution and sex incidence were reviewed.