ABSTRACT.The testicular volumes (V) of 817 adult (non‐Down's syndrome) institutionalized males were calculated. The mean testicular volume was 19.5±15.8 ml, comparable to the normal adult male mean of 17–19 ml. However, the number of institutionalized males with V≤25 ml and V≤10 ml was increased approximately fourfold over the normal male population. Resident adult males were grouped into three categories based on their testicular volumes: (1) V≤25 ml (macro‐orchid); (2) V≤15 ml (micro‐orchid); and (3) 15