Puberty is the gradual transition period between childhood and adulthood. Many factors may contribute to the onset of puberty. The objective of the study was to determine the age of onset of secondary pubertal characteristics among Saudi Arabian girls. A cross-sectional study was conducted using a cluster sample design. Seven hundred and twenty-five schoolgirls between the ages of 6 and 16 years from diverse socioeconomic levels were included. During physical examinations, the height and weight of the girls were recorded, and the stages of breast and pubic hair development were determined according to Tanner stages; axillary hair development was determined according to modified stages. The median age at Tanner stage 2 for breast and pubic hair development was 10 years. The median age at stage 2 in modified scales for axillary hair development was 12 years. In conclusion, the median age of the onset of breast development at Tanner stage 2 for Saudi girls in Riyadh is lower than what has been reported in some countries in Europe, South Africa, Turkey and India but similar to girls in Hong Kong, China and white girls in the USA, which may support secular trends of an earlier onset of puberty.