A 16½-year-old male gorilla died unexpectedly and suddenly. He had thrombophlebitis, estimated at one month duration, involving his left leg, pelvic veins and inferior vena cava. Death was due to fracture of the larynx with hemorrhage into the neck, resulting in asphyxia. A most important finding was immaturity and atrophy of the spermatogenic portion of the testes with normal or increased interstitial cells. Bobo did not have a proven sex chromosome abnormality but he did have a few cells with a 49 chromosome count, suggesting mosaicism for an autosomal chromosome. Testicular atrophy in gorillas has been reported frequently. It is suggested that further investigation of testicular abnormality in the gorilla may offer some explanation for their relative infertility