Introduction: Klinefelters syndrome (KS) is the most common cause of male hypogonadism. It is also the most common sex chromosome disorder among men. Key clinical features of KS are small testes, gynaecomastia and long legs. It is known to be associated with other conditions like mitral valve prolapse, varicose veins, breast cancer and autoimmune diseases1. Rarely it can be associated with thalassemia2. Here we are reporting a similar rare association of KS with thalassemia major. Case report: A18 years old boy presented with poor development of secondary sexual characteristics. He was born out of non-consanguineous marriage with no significant perinatal events. At 4years of his age, he was evaluated for easy fatigability, tiredness and weakness and found to have anemia. On further work-up, it turned out to be thalassemia major and both parents were found to have thalassemia trait. Since then, he is on regular blood transfusion and iron chelating therapy. However he stopped iron chelating therapy recently. From last three years he noticed bilateral enlargement of breast. On examination he had small testes, under developed pubic hair, bilateral gynaecomastia, long legs and hepatic enlargement. Laboratory evaluation showed low testosterone (237ng/dL), elevated follicular stimulating hormone (FSH -68mIU/mL), luteinizing hormone (LH- 62mIU/mL), which is indicative of primary gonadal failure. His karyotype was 47,XXY. Diagnosis of Klinefelters syndrome was made based upon clinical and laboratory findings. Other laboratory tests showed: hemoglobin - 11.7g%, fasting blood sugar (FBS)- 92mg/dL, serum calcium- 9mg/dL, and normal renal and liver function tests. Other hormonal tests such as thyroid profile, prolactin, serum estradiol and serum cortisol were normal. His serum ferritin was high (5671ng/mL) as hehad stopped iron chelating therapy. In our patient, cause of hypogonadism was primary testicular failure due to KS. Our patient has KS associated with thalassemia major, which is a rare association. In thalassemia, hypogonadism results from iron over load and hypogonadotropic hypogonadism often responsible for this. Even though serum ferritin elevated it has not resulted in any impact on gonadotropic hormones and this might be due to short time interruption of iron chelating therapy. Conclusion: In our patient delayed puberty was due to KS. Association of KS with thalassemia major is very rare. To our knowledge this is the first case report on KS associated with thalassemia major.