AbstractPenile lengths of Japanese males from birth to adolescence were studied in cross‐sectional series. The mean length of the penis in 5 days term newborn was 2.9 ± 0.5 cm (M ± SD). There was a gradual increase in penile length from the age 1 to 11 years. After 12 years of age there was a sudden increase in length. The mean length increased from 5.5 ± 1.5 cm at the age of 12 to 8.3 ± 0.8 cm at 14 years. The largest increment was observed between the age of 13 and 14 years. Mean penile length increased from 4.9 ± 0.8 cm at stage I of pubic hair development to 7.2 ± 1.4 cm at stage II and 9.0 ± 1.0 cm at stages IV‐V. The largest increment was observed between stage I and stage II of pubic hair development. This new reference of penile length can be helpful in those cases in which the children is suspective of having genitals of abn