Spontaneous endometriosis in a cynomolgus monkey (Macaca fascicularis).

An adult female Macaca fascicularis developed anorexia and minimal fecal production. Abdominal palpation was unrewarding. Rectal palpation revealed a rectal stricture and a large soft tissue mass in the area of the uterus. Clinical pathology tests were within normal limits. Exploratory surgery and histopathology confirmed a diagnosis of endometriosis.