Tracking secular trends in the pubertal development of a country's children is important for social and public health reasons. Although comparable studies are largely lacking for US children over the last half century, existing data on girls, particularly that for menarche, indicate that the trend for earlier sexual maturatin has continued and that racial differences are significant, with African-American girls developing earlier than white girls. Data on boys, though less reliable, suggest that they may be beginning maturation earlier as well. More studies on boys with reliable methodologies are needed. Earlier development may not be healthy and may indicate environmental problems that need to be further researched and addressed.