Stage 1: no pubic hair and no enlargement of penis or testes (testes <2.5cm in longest diameter). Stage 2: testicular enlargement to >2.5cm, and thinning and reddening of the scrotal skin occur; slightly dark and curly hair appears at the base of the penis. Stage 3: phallic enlargement in length and width occurs, with increasing testicular size; pubic hair is coarser, darker, and curlier, with spread. Stage 4: further darkening of the scrotum and enlargement of the testes and penis; hair is adult in type but does not spread to the thighs. Stage 5: adult genital appearance is achieved; hair is spread to the medial surface of the thighs. Reproduced from Tanner ( 1962), by courtesy of Blackwell Scientific Publications.
