Micropenis is usually defined as a penis that has a stretched length less than 2.5 standard deviations below the mean value. The purpose of this study was to establish a database and set referable standards of penile length for Taiwanese boys. METHODS: A total number of 2126 boys (156 male newborns, 1198 male infants under 2 years old, and 772 boys older than 2 years old) were included in this study. We excluded those boys with congenital anomaly, frankly genital anomaly and congenital heart disease. Both stretched and flaccid penile lengths were measured for comparison. RESULTS: Our data revealed that the average penile length increased with chronologic age (about 3 cm in neonates, 4 cm when 1 year old, and near 5 cm when 5 years old). But it also revealed that Taiwanese boys have slightly shorter stretched penile length after newborn period till 5 years old when compared with Caucasian boys (all P values < 0.05). CONCLUSIONS: Normal stretched penile length varied between different ethic groups, and maybe body size contribute more or less to smaller penile size in Taiwanese boys compared to Caucasian boys in light of general knowledge that Caucasian is taller than Chinese (including Taiwanese) in average.