Puberty describes the complex physiological transition between childhood and adulthood. Dramatic physical changes occur, most notably the development of secondary sexual characteristics and the pubertal growth spurt. During the adolescent growth spurt, growth velocity increases from pre-pubertal rates of 4-6 cm per year to as much as 10-15 cm per year. Accompanying the increase in gonadal steroids is an increase in amplitude of growth hormone secretory bursts. Evidence suggests that adequate growth hormone and gonadal steroids are both necessary for the attainment of a normal pubertal growth velocity, and the complex interplay between these two hormonal axes is under intense investigation. Delayed onset of puberty, or constitutional delay of growth and adolescence, is a common phenomenon presenting particularly in boys. Physiologically, it represents an extension of the normal pre-pubertal hypogonadotropic hypogonadal state. Without intervention, these children will spontaneously undergo puberty and often reach their genetic height potential, but their delay compared with that of their peers is often of concern to the children and their families. Recent evidence suggests long-term physiological benefits of early androgen replacement therapy in these boys, including maximizing attained bone mineral density. Androgen replacement therapy in male adolescents with constitutional delay of growth and adolescence is beneficial psychologically as well as physiologically and should be initiated promptly.