Acromegaly is a rare disorder usually caused by a benign tumour of the pituitary gland. Long-term presence of elevated growth hormone (GH) and insulin like growth factor 1 (IGF1) levels accompanying this disease is associated with complications such as cardiomyopathy, diabetes mellitus, sleep apnoea and arthropathy. Incidence of acromegaly is 3-4 patients per million per year. Klinefelter syndrome (KS) is the most common sex chromosome disorder occuring in about 1/500 live male births. Common physical features include particularly small testes, among other symptoms are tall stature, reduced muscle tone, delayed pubertal development, lack of secondary male sex characteristics and gynecomastia. We present a 32-year-old man suffering from both acromegaly and 47, XXY Klinefelter syndrome. The patient with typical acromegalic features. Laboratory tests revealed high level of GH which was not suppressed after glucose administration, high level of IGF1, low testosterone concentration with high concentation of luteinizing hormone and follicle stimulating hormone. A magnetic resonance imaging scan revealed a 25 × 18 × 18 mm macroadenoma involving the pituitary gland. A diagnosis of acromegaly was established. After this examination trans-sphenoidal resection was performed. Histopathologic and immunohistochemical findings revealed growth hormoneproducing pituitary adenoma. The presence of infertility with clinical features such as small testes, lack of secondary male sex characteristics and laboratory findings revealed hypergonadotropic hypogonadism that could not be explained by the diagnosis of acromegaly. A chromosomal karyotyping revealed a 47, XXY, confirming the diagnosis of KS. Testosterone replacement therapy wasn´t begun because of patient disagreement Postoperatively elevated plasma concentration of GH and IGF1 levels persist. Treatment by somatostatin analogues (lanreotid) was initiated at dose 120 mg every 28 days. Control magnetic resonance imaging of the sella demonstrated a residue of pituary adenoma size 14 × 14 × 7 mm. The patient is currently undergoing endoscopic revision of the residue. acromegaly - growth hormone - IGF1 - Klinefelter syndrome - testosterone.