ABSTRACT
Klinefelter syndrome is the most common sex chromosome disorder in males. Variation in clinical presentation and insufficient awareness of this syndrome among clinicians lead to fifty percent of patients remain undetected. Typical clinical features of Klinefelter syndrome are various degrees of hypogonadal symptoms, atrophic testes and gynaecomastia. However, these typical clinical symptoms may not be present in all patients. Even if serum testosterone levels are not markedly low, elevated serum follicle-stimulating hormone is a considerable laboratory finding. Definitive diagnosis is made by karyotype analysis of peripheral blood lymphocytes. It must be kept in mind that this analysis may be normal in rare conditions. Early recognition of patients during puberty and handling them as soon as possible is important. Testosterone replacement therapy results in increased muscle mass, bone mineral density and libido. The patient’s mood and self-esteem improve significantly. In general, patients with Klinefelter syndrome are accepted as infertile, however, assisted reproductive techniques may provide fertilization.