Clinicians have long suspected that tongue shape differs between obstructive sleep apnea (OSA) patients and normal subjects. The purpose of this study was to determine whether such differences exist. Because of the difficulty in specifying reproducible homologous landmarks for the tongue, a morphometric technique-the eigenshape analysis-was used. The eigenshape analysis transforms an outline contour into a set of discrete numbers that are tangent angles of the curvature along the outline at each digitized point on the outline. Pairs of cephalograms were taken of 80 male patients in upright and supine positions. The subjects were subgrouped into four categories according to severity of symptoms. The contour of the tongue was traced, digitized, and subgrouped. When the major portion of the tongue shape variations in the supine position were graphically compared between subgroups, variations in the nonapneic group were distinguished from those in the apneic groups. The results suggest that the eigenshape analysis on cephalograms in the supine position may be a useful tool to distinguish OSA subjects from nonapneic subjects.