Patients with complete unilateral cleft lip and palate (UCLP) display considerable variability in clinical presentation. This variability relates to presentation at birth, later observed dento-alveolar and skeletal craniofacial deficiencies, response to treatment, and post-treatment stability. Possible factors affecting later observed variability are genetics, function, and iatrogenic influences. The present objectives were to investigate 1) possible associations between the severity of the cleft lip deficiency in patients with UCLP and variations in dento-facial growth and development, and 2) whether variation in stability following orthognathic surgery to permit adequate functional jaw relations and harmonious facial esthetics could be explained by the magnitude or segmentation of maxillary advancement. The results suggest that children with a more severe form of UCLP at infancy are susceptible to tooth agenesis in the cleft area, poorer dental arch relationships, and more deficient maxillary growth. The stability of maxillary advancement appears to be independent of magnitude or segmentation.