Klinefelter syndrome is not easy to diagnose in childhood because of the absence of significant manifestations before puberty. Three main clinical signs should suggest the diagnosis in a child: small testes, tall stature, and mental retardation or learning problems. We present a patient with Klinefelter syndrome and short stature due to growth hormone deficiency. His height was below the third percentile for age and his bone age delayed. Maximal serum GH levels after insulin-induced hypoglycemia and clonidine were low, demonstrating GH deficiency. He received growth hormone treatment with good response. The diagnosis of Klinefelter syndrome was made at puberty, because the patient did not present a normal progression of testicular development and puberty. At that moment, a karyotype was made confirming the suspected diagnosis. We wish to emphasize the rare association between Klinefelter syndrome and growth hormone deficiency.