During puberty, estrogen has a biphasic effect on epiphyses; at low levels, it leads to an increase in height and bone mass, whereas at high levels, it leads to closure of the epiphysis. Tamoxifen is a selective estrogen receptor modulator that has been used in the treatment of pubertal gynecomastia. Although it has not been approved for this indication, studies have shown it to be both successful and safe. In males, the peak of pubertal bone development occurs during Tanner stage 3-4, which is also when pubertal gynecomastia reaches its highest prevalence. Thus tamoxifen treatment could potentially effect pubertal bone development. The aim of this study was to assess the effects of tamoxifen on bone mineral density (BMD) and skeletal maturation when used for pubertal gynecomastia. We evaluated 20 boys with pubertal gynecomastia receiving tamoxifen for at least 4 months. BMD was measured with dual-energy X-ray absorptiometry. Z-score and absolute BMD (g/cm(2)) was determined at baseline and 2 months after completing tamoxifen treatment. Bone age and height was evaluated before treatment and again one year later. Using absolute BMD (g/cm(2)), the mean difference from baseline was significant between the two groups both at spine (p = 0.002) and femur (p = 0.001), but not with the Z-score. This result was attributed to the expected increase during puberty according to sex and age. No significant effect on skeletal maturation was found (p = 1.112). We conclude that when pubertal bone development is concerned, tamoxifen is safe for the treatment of pubertal gynecomastia as neither bone mineralization nor growth potential was affected.