by Nicole Evans M.D.

Created on: December 29, 2009   Last Updated: January 22, 2010

Sexual development in boys occurs in predictable stages.  J.M. Tanner divided the visible changes of puberty into five stages and published his work back in 1962. Since that time, the stages of pubertal development in boys have become known as The Tanner Stages.

There are 5 Tanner Stages of sexual development in boys.  The ability to have predictable stages of puberty is particularly useful for physicians.  Physicians identify which Tanner stage a child is in as a means to determine if the child is developing appropriate physical sexual characteristics at the appropriate age.  For example, a 6 year old boy with sexual characteristics of Tanner stage 2 may have precocious puberty and need further medical work up.

Certain aspects of sexual development are shared between boys and girls. These include adrenarche (or pubarche) which is the appearance of pubic hair, and a growth spurt. Additional stages of sexual development, not considered in the Tanner stages, occur predictably in boys and girls. For example, menarche (onset of menses) in girls and nocturnal emissions (wet dreams) in boys.  Nocturnal emissions and a growth spurt can occur relatively early. Once the growth spurt reaches its peak, it will continue at a slower pace for several years.

The overall sexual development of boys occurs in a regular sequence of events. However, this sequence lacks the cut and dry milestones so obvious in female sexual development. Testicular enlargement starts early and the testicles continue to enlarge while the other sexual changes begin.  Adrenarche (pubic hair development) usually precedes penile enlargement.  The increase in penile length and width is complete once Tanner Stage 5 is reached (see below).

Tanner Stage 1 in Boys:

Penis, testes, scrotum- childhood size

Pubic hair- no pubic hair

Tanner Stage 2 in Boys:

Penis, testes, scrotum- enlargement of testes, scrotal skin reddens

Pubic hair- sparse growth of long, slightly pigmented, straight or minimally curled hair that grows primarily at the base of the penis.

Tanner Stage 3 in Boys:

Penis, testes, scrotum- further growth of testes and scrotum with enlargement of the penis, mainly in length.

Pubic hair- hair becomes darker, coarser and curlier

Tanner Stage 4 in Boys:

Penis, testes, scrotum- further growth of testes and scrotum with enlargement of the penis, especially in width.

Pubic hair- adult type pubic hair covers an area smaller than in the adult and does not extend onto the thighs.

Tanner Stage 5 in Boys:

Penis, testes, scrotum- genitalia are adult in both size and shape.

Pubic hair- the hair is adult in quantity and type and extends on to the thighs.

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