Normal growth during adolescence includes both an increase in body size and sexual maturation (puberty). The timing and speed with which these changes occur vary and are affected by both heredity and environment. During adolescence, boys and girls reach adult height and weight. The growth spurt in boys occurs during mid-adolescence between the ages of 12 and 17 years. Boys grow about 4 inches (about 10 centimeters) during their year of maximum growth. The growth spurt in girls occurs in early adolescence between the ages of 9½ and 14½ years. Girls grow about 3½ inches (about 9 centimeters) during their year of maximum growth. In general, boys become heavier and taller than girls. By age 18, boys have about ¾ inch (about 2 centimeters) of growth remaining and girls have slightly less.

Puberty also occurs during adolescence. In boys, the first signs of puberty are enlargement of the scrotum and testes, followed by lengthening of the penis. Internally, the seminal vesicles and prostate gland enlarge. Next, pubic hair appears. Hair grows on the face and in the underarms about 2 years after it appears in the pubic area. Ejaculation may begin in mid-adolescence (around age 12½ to 14 years), about 1 year after the penis begins to lengthen. Fertility, however, is not attained until later in adolescence. Breast enlargement (gynecomastia) on one side or both is common among young adolescent boys and usually disappears within a year.

In the majority of girls, the first visible sign of puberty is breast budding, although in many girls the growth spurt can occur up to a year before. Soon after breast budding, pubic and underarm hair appears. The first menstrual period (menarche) occurs within a wide range (typically between ages 10 and 16 years), with most girls in the United States starting their periods at 12 or 13 years. Timing is influenced by genetics, ethnicity, nutrition, and other factors. Puberty begins earlier today than it did a century ago. For example, the average age of the first menstrual period (menarche) has decreased by about 3 years over the past 100 years. The reasons probably include improvements in nutrition, general health, and living conditions.

Milestones in Sexual Development During puberty, sexual development occurs in a set sequence. However, when the changes begin and how quickly they occur vary from person to person. For girls, puberty begins at age 8½ to 10 years and lasts about 4 years. For boys, puberty begins at age 9½ to 10½ years and lasts about 3 years. The chart shows a typical sequence and normal range of development for the milestones of sexual development.

Even during normal adolescence, substantial emotional adjustments are required. If the timing is not typical, particularly in a boy whose physical development is delayed or a girl whose development occurs early, additional emotional stress is likely. Most boys who grow slowly eventually attain normal height. However, adolescents whose growth or sexual development is delayed should be evaluated to rule out diseases and other physical causes and given reassurance if the evaluation is negative.

Last full review/revision February 2009 by Sharon Levy, MD, MPH