Aim: With the high prevalence of postmenopausal osteoporosis in Saudi Women (1), among other factors, failure to achieve peak bone mass (PBM) during puberty was suggested to be the culprit. Bone physiology parameters of a representative sample of adolescents in Jeddah were studied. Materials and Methods: Three hundred three adolescents (13-19 years) were selected from seven PHCC by multistage cross-sectional sampling and were studied prospectively. Demographic data, dietary habits, and lifestyle parameters were obtained by direct interview. Serum samples of calcium, phosphate, alkaline phosphatase, parathormone, 25 OH vitamin D, and osteocalcin were collected. Statistical analysis was done using SPSS 16. Results: The mean value of 25-hydroxy-vitamin D was 32.55 (50-75) nmol/ml with 89.5 % of the 303 adolescents with insufficient levels (< 50 nmol/L). There was a significant inverse correlation of serum parathormone with 25-hydroxy-vitamin D and calcium (p = 0.000 and p = 0.003), but no significant correlation of osteocalcin with 25 OH vitamin D. Linear regression of osteocalcin and the independent variables revealed no significant effect. Conclusion: Although 25 OH vitamin D levels were less than desirable in almost all adolescents, bone formation marker was normal. Could different genetic factors or microenvironment molecules have effect on bone physiology of Saudi girls? Future longitudinal studies are needed.