Objectives: The objectives of this study were to evaluate the long-term effects of orchidectomy and low testosterone on the craniofaciodental development and maintenance of skeletal and oral health in rhesus macaques. Materials and Methods: Mandibles of four castrated and intact age-matched male rhesus monkeys (Macaca mulatta) from Cayo Santiago were compared for mandibular morphology and teeth, abnormalities, pathology, and cortical bone thickness and density using a digital sliding caliper and analysis of three-dimensional X-ray images. Results: Although all four castrates were generally comparable to intact males in overall mandible and teeth size, there were some significant differences. In the castrates, (1) the distance between the two rami was narrower than in intact males leading to a relatively narrower and longer face; (2) both the mandibular body and ramus had thinner cortical bone leading to less total bone mass; and (3) the canines and molar teeth were slender with lower and less robust tooth cusps. In addition, the alveolar bone of two geriatric castrates was greatly receded with signs of periodontitis more severe than in intact aged males. Old castrates also had severe temporomandibular joint osteoarthritis. Discussion: The findings suggest the importance of testosterone in craniofaciodental development, and maintenance of skeletal and oral health in male macaques. These results suggest that dental health professionals might want to include in their medical history questionnaires whether or not male patients have taken hormone (testosterone) replacement therapy. (c) 2015 Wiley Periodicals, Inc.