The clinical manifestations of Klinefelter syndrome can vary significantly, depending on the individual's chromosomal makeup and the presence of mosaicism or variant forms. While infants and children with Klinefelter syndrome typically exhibit normal height, weight, and head circumference, a characteristic tall stature with disproportionately long limbs relative to the torso often emerges after puberty. Some individuals may experience mild developmental delays, behavioral challenges, and learning difficulties. Approximately half of those affected may present with mitral valve prolapse, a cardiac condition. There is an increased risk of developing autoimmune conditions, such as rheumatic diseases, thyroid disorders, and diabetes mellitus. Reduced testicular size often leads to lower testosterone levels and a resulting imbalance in other hormone profiles. This hormonal imbalance can manifest as gynecomastia (breast tissue enlargement) towards the end of puberty, which, in turn, increases the risk of breast cancer up to 20-fold in these patients. Infertility and azoospermia are common findings, although these may be less severe or even absent in individuals with mosaic forms of the syndrome. The diagnosis is frequently made during investigations for male infertility, underscoring the importance of recognizing these varied symptoms.