Twenty-four ill or dead desert tortoises (Gopherus agassizii) were received between March 1992 and July 1995 for necropsies from the Mojave and Colorado deserts of California (USA). Diseases observed in these animals included cutaneous dyskeratosis (n = 7); shell necrosis (n = 2); respiratory diseases (n = 7); urolithiasis (n = 3); and trauma (n = 5). In tortoises with cutaneous dyskeratosis the horn layer of shell was disrupted by multiple crevices and fissures and, in the most severe lesions, dermal bone showed osteoclastic resorption, remodeling, and osteopenia. In tortoises with shell necrosis, multiple foci of necrotic cell debris and heterophilic inflammation within the epidermal horn layer were subtended by necrotic dermal bone colonized by bacteria and fungi. Of the seven tortoises with respiratory disease, five were diagnosed with mycoplasmosis. The diagnosis of mycoplasmosis was based on the presence of chronic proliferative rhinitis and positive serologic tests and/or isolation of Mycoplasma sp. Chronic fungal pneumonia was diagnosed in one tortoise with respiratory disease. In the three tortoises with urolithiasis, two were discovered dead, and the live tortoise had renal and articular gout. Traumatic injuries consisted of one tortoise entombed within its burrow, one tortoise burned in a brush fire, two tortoises struck by moving vehicles, and one tortoise attacked by a predator. While the primary cause of illness could be attributed to one or two major disease processes, lesions were often found in multiple organ systems, and a variety of etiologies were responsible for morbidity and mortality.