49,XXXXY syndrome is a very rare condition that is associated with a considerable more severe phenotype than classic 47,XXY Klinefelter syndrome. We present a patient with 49,XXXXY syndrome, who was first presented to an endocrinological unit at the age of 12.5 years with prepubertal genitalia. He was then lost from follow-up and showed clear clinical and biochemical signs of hypergonadotropic hypogonadism when presenting again at the age of 16 years. The patient was started on testosterone replacement therapy. This case is reported to underline the need for thorough endocrinological follow-up examinations in males with X polysomies.