Forty-three patients with the androgen insensitivity syndrome (AIS), ages 14 to 83 (average 27) years, were studied. Forty patients had complete AIS and three patients had incomplete AIS. Microscopic examination of the testes revealed immature tubules, which contained rare spermatogonia in 28% of the cases. Prominent Leydig cells and a spindle-cell stroma resembling ovarian stroma were found in a majority of cases. The organization of the testicular parenchyma could be classified into one of four patterns: diffuse tubulostromal, lobular tubulostromal, mixed tubulostromal, or stromal-predominant. Hamartomas were present in 63% and Sertoli cell adenomas in 23% of the cases. Malignant tumors developed in 9% of the patients and comprised two seminomas, one intratubular germ cell neoplasm with early stromal invasion, and a malignant sex cord tumor. At least one fallopian tube was present in 35% of the cases.