Background: A secular trend towards a younger age of puberty onset has been reported in Chilean girls. Aim: To evaluate the age of onset of puberty and prevalence of early puberty in Chilean boys. Material and methods: A pediatric endocrinologist examined 319 children attending schools in central Santiago. Pubertal development was assessed by testicular volume (TV) and genital inspection (GI) using Tanner graduation. Precocious and early puberty development was diagnosed if TV ?4 ml or GI >stage 2 occurred in boys younger than 9 years and at 9-10 years of age, respectively. Results: Pubertal onset occurred at 10.2± 1.5 years according to TV and at 11.1±1.6 years according to GI (p < 0.01). Before the age of nine, 15.2% of children had a VT ? 4 ml, 3% had genital changes in GI and only 3% had both changes simultaneously. Early puberty was observed in 23.8% of children according to TV and 9.5% according to GI. However, no child of less than 11 years old had a TV ? 4 ml, genital changes and pubic hair simultaneously. Late pubertal stages occurred at the same age according to both criteria used. Body mass index z score was not associated with the age of pubertal onset. Conclusions: Testicular enlargement occurs one year earlier than changes in genitalia according to inspection. Testicular growth, but not late stages of puberty, are occurring one year earlier than previously reported in Chile 10 years ago.Background: A secular trend towards a younger age of puberty onset has been reported in Chilean girls. Aim: To evaluate the age of onset of puberty and prevalence of early puberty in Chilean boys. Material and methods: A pediatric endocrinologist examined 319 children attending schools in central Santiago. Pubertal development was assessed by testicular volume (TV) and genital inspection (GI) using Tanner graduation. Precocious and early puberty development was diagnosed if TV ?4 ml or GI >stage 2 occurred in boys younger than 9 years and at 9-10 years of age, respectively. Results: Pubertal onset occurred at 10.2± 1.5 years according to TV and at 11.1±1.6 years according to GI (p < 0.01). Before the age of nine, 15.2% of children had a VT ? 4 ml, 3% had genital changes in GI and only 3% had both changes simultaneously. Early puberty was observed in 23.8% of children according to TV and 9.5% according to GI. However, no child of less than 11 years old had a TV ? 4 ml, genital changes and pubic hair simultaneously. Late pubertal stages occurred at the same age according to both criteria used. Body mass index z score was not associated with the age of pubertal onset. Conclusions: Testicular enlargement occurs one year earlier than changes in genitalia according to inspection. Testicular growth, but not late stages of puberty, are occurring one year earlier than previously reported in Chile 10 years ago.