49,XXXXY and 45,X syndromes are sex chromosome aneuploidies in which the affected individuals present with hypergonadotropic hypogonadism, short or long stature, and skeletal malformations. Psychological, endocrinological, and orthopaedic disorders constitute the major problems in the clinical follow-up. We report a family with two rare entities: 49,XXXXY and 45, X. Sex chromosome abnormalities should especially be in mind in the evaluation of patients with micropenis, mental retardation, and hypergonadotropic hypogonadism. Management mandates a multidisciplinary approach with pediatric endocrinology, pediatric surgery, orthopaedics, psychiatry, and clinical genetic evaluations. To our knowledge, our cases are the first to report the sibling patients with 49,XXXXY and 45,X.