A series of testicular fine-needle aspiration biopsy specimens from 272 infertile men with azoospermia were reviewed and categorized according to morphologic patterns. These included active spermatogenesis, 14 (5%); hypospermatogenesis, 106 (39%); Sertoli cells only, 70 (26%); atrophic pattern, 52 (19%); and maturation arrest, 1 (0.36%). In 29 cases (11%) the amount of material was insufficient for evaluation. The histologic and cytologic findings in 52 cases showing spermatogenesis correlated very well in 52 cases for which open testicular biopsy specimens were also available. These findings indicate that fine-needle aspiration biopsy of the testis is a reliable and useful technique for the investigation of patients with azospermia.