RESUMEN
Klinefelter syndrome (KS) is one of the most common disease entities characterized by X-chromosomal aberration causing the primary hypogonadism in adult men. Patients with KS seem to be typically characterized by tall, slender bodies with delayed puberty and hypergonadotropic hypogonadism. However, it has been known that they have a broad spectrum of phenotype ranging from almost normal external appearances to typical phenotype. Only 25% KS Patients are ever diagnosed because KS remains unrecognized. Also, boys with KS have an onset of pubertal development within the normal range, not delayed onset of puberty. Adolescents with KS are generally diagnosed as having the lack of pubertal progress. Early detection of KS can be difficult without awareness. We report an unusual case of early onset of puberty in obese boy with KS who presented with a unilateral non-hormone secreting testicular teratoma.