Hi, Welcome to HCM. I have gone through your question and understand your concerns. Breast development in a 15 yr old can be 1. Physioogical - due to normal hormonal changes in body 2. Pathological - due to abnormal hormones in body This needs evaluation. The breast development can be due to 2 hormones Estrogen (female hormone) and Prolactin. This is stopped by testosterone (male hormone). When the Estrogen / testosterone ratio is high this result in breast development in males. This could be due to decreased testosterone production or increased estrogen production 1. Physiological breast development: In puberty by 13-15 years, males start producing small amount of testosterone. This testosterone is partially converted to estrogen in body fat. So there can be a small breast development in puberty which is more in fatty children. Once more and more testosterone is produced this will suppress breast development. So this breast development will be there for 6-12 months only 2. Pathological gynaecomastia This can be due to excess estrogen or prolactin produced in body or decreased testosterone produced. In a similar case what I will do is a clinical examination to see how his penile size, testes size and sexual hair is, & check whether the breast develop is truely breast or fat. The hormonal tests are planned after clinical examination. Usual tests that are done are testosterone, FSH, estradiol, prolactin, beta HCG and thyroid function tests. This is fixable. If hormonal tests are abnormal medical management is there to fix the problem. If every tests are normal, then medications or surgical correction can be done. Hope I have answered your query. If you have any further questions I will be happy to help With warm regards, Dr Ajish TP (MD,DM) Consultant Endocrinologist.