The aim of this study was to evaluate bone mineral density and some markers of bone metabolism (alkaline phosphatase activity, osteocalcin concentration, deoxypirydinoline excretion), as well as the influence of physical activity and dietary calcium supplementation on bone density and bone metabolism in boys with a constitutional delay of growth and puberty (CDGP), in relation to calendar age, bone age and pubertal stage. The study was done in 41 boys aged 8-18 years with CDGP diagnosed on the basis of family history and typical pattern of growth, with prior exclusion of hormonal and non-hormonal causes of height deficiency. According to Tanner's criteria, boys were assigned to 4 groups corresponding to 4 stages of puberty (Tab. 1). Total body (total BMD) and lumbar spine (L2L4 BMD) bone mineral density were obtained using DEXA densitometry. The activity of alkaline phosphatase (AP) and serum osteocalcin (OC) concentration served as markers of bone formation. 24-h urinary deoxypirydinoline (DPD) excretion was a marker of bone resorption. Using a questionnaire, daily dietary calcium intake and physical activity were established. A positive correlation between calendar age, total BMD and L2L4 BMD was found (R = 0.70 and R2 = 0.49; R = 0.72 and R2 = 0.51; p < 0.001, respectively). Bone age was positively correlated with total BMD and L2L4 BMD (for both correlations R = 0.68, R2 = 0.47; p < 0.001). Total BMD adjusted for calendar age revealed osteoporosis in 4 cases (9.7%), osteopenia in 19 cases (46.3%) and normal bone density in 18 cases (43.9%). After adjustment of BMD to bone age, 2 boys (4.9%) were diagnosed with osteoporosis, 9 (21.9%) with osteopenia, and 30 (73.2%) with normal bone density. L2L4 BMD adjusted for calendar age showed osteoporosis in 6 cases (14.6%), osteopenia in 21 cases (51.2%) and normal density in 14 cases (34.2%). After adjustment of BMD to bone age, 3 boys (7.3%) were diagnosed with osteoporosis, 10 (24.4%) with osteopenia, and 28 (68.3%) with normal bone density. A significant correlation between stage of puberty, total BMD (p < 0.045) and L2L4 BMD (p < 0.001) was found. Values for total BMD and L2L4 BMD in boys with CDGP in relation to pubertal stage are presented in Table 2. Mean AP activity, serum OC concentration, DPD excretion, dietary calcium intake and physical activity in boys at consecutive stages of puberty are presented in Table 3. No significant correlation between pubertal stage, markers of bone metabolism, daily dietary calcium intake or physical activity was found. The boys were next grouped according to level of physical activity: low (< 10 h/week) or high (> 10 h/week). Table 4 summarizes the results for both groups. No significant differences between the groups were found concerning the parameters studied. Two groups with a low (< 1.2 g) and high (> 1.2 g) dietary calcium intake were also formed. The results for both groups are presented in Table 5. A significant correlation between dietary calcium intake and total BMD (R = 0.34 and R2 = 0.11; p < 0.03) was revealed. On the basis of these results it can be concluded that BMD values in boys with CDGP should be adjusted for bone age, thus significantly limiting the diagnosis of osteoporosis and osteopenia. BMD values for these boys increase with consecutive pubertal stage, while markers of bone metabolism do not reveal significant abnormalities (markers of bone formation increase until stage IV, markers of bone resorption show fluctuating values).