Differences in craniofacial morphology between complete and incomplete unilateral cleft lip and palate were studied in adult males by roentgenocephalometry. Incomplete clefts did not have the widening of the nasal cavity, reduction of the upper face height, or reduced thickness of the upper lip found in complete clefts. The shortening of maxillary depth was half that noted in complete clefts. The mandibular deviations and interorbital widening did not differ. The same held true for the retroinclination of upper incisors and alveolar process and backward shift of the maxilla. These changes accounted for differences in sagittal maxillo-mandibular relations, facial profile, occlusion of incisors and total facial height between complete and incomplete clefts. Limitation of anterior growth rotation of the face was identical. The independence of mandibular variations on the extent of the cleft and on maxillary malformation suggests the possibility of an underlying primary impairment of growth of the lower jaw, at least in some cases.