Adequate dietary intake during the growth period is critical for bone mineral accretion. In 1997, an adequate intake (AI) of 1300 mg/d Ca was set for North American adolescents aged 9-18 years based on best available data. We determined bone Ca accrual values from age 9 to 18 years taking into account sex and maturity. Furthermore, we used the accrual data to estimate adolescents' Ca requirements. Total body bone mineral content (TBBMC) of eighty-five boys and sixty-seven girls participating in the Saskatchewan Paediatric Bone Mineral Accrual Study were used to determine annual TBBMC accumulation over the pubertal growth period. Using a similar factorial approach as the AI, we estimated Ca requirements of adolescent boys and girls for two age groups: 9-13 and 14-18 years. Between 9 and 18 years, boys accrued 198.8 (SD 74.5) g bone mineral content (BMC) per year, equivalent to 175.4 (SD 65.7) mg Ca per d with the maximum BMC accrual of 335.9 g from age 13 to 14 years. Girls had 138.1 (SD 64.2) g BMC per year, equalling121.8 (SD 56.6) mg Ca per d with the maximum annual BMC accrual of 266.0 g from age 12 to 13 years. Differences were observed between both sex and age groups with respect to Ca needs: boys and girls aged 9-13 years would require 1000-1100 mg/d Ca, and from age 14 to 18 years, the mean Ca requirements would be relatively stable at 1000 mg/d for girls but would rise to 1200 mg/d for boys.