Coat damage has been reported frequently in captive rhesus macaques (Macaca mulatta), and it is a serious health problem because the hair coat functions as an anatomic and physiologic barrier between the animal and the environment. The purpose of this study was to identify the pathogenesis of coat damage in this species and to exclude the most frequent causes of alopecia. The investigation included clinical, hematologic, bacteriologic, mycologic, parasitologic, and histopathologic evaluations. A broad systematic dermatologic investigation was performed on 156 rhesus macaques, kept under variable environmental conditions, at the German Primate Center, Göttingen. In addition, 27 animals from other primate facilities were incorporated into the study. Clinically, 126 animals showed partial alopecia of varying severity, with complete alopecia in the worst cases. In 88% of the cases, the disorder was bilaterally symmetrical. The back and extremities were most commonly affected. No gross clinical changes of the skin surface were detected. Histologic changes consisted predominantly of mild epidermal hyperkeratosis and mild perivascular dermatitis. The presence and severity of histologic lesions were not correlated to coat damage. Parasitic, bacterial, and mycotic causes of alopecia were ruled out. Overviewing these results, disturbances in environment and behavior controlling or influencing hair growth may lead to hair loss in captive rhesus macaques. Future studies should try to identify disturbances in extrinsic or intrinsic factors influencing hair follicle activity in rhesus macaques.