The purpose of this work is to present the most common sex chromosome aneuploidies and to discuss their diagnosis, etiology, epidemiology, and pathophysiology, as well as the most frequent clinical presentation and lifelong care organization. Aneuploidies of sex chromosomes are numerical chromosomal aberrations that result in the loss or gain of one or more sex chromosomes. The most common aneuploidies of sex chromosomes are Klinefelter syndrome (47,XXY), Turner syndrome (45,X), Triple X syndrome (47,XXX), and XYY syndrome (47,XYY). X chromosome inactivation occurs to equalize gene dosage between sex chromosome genes and the rest of the genome. However, certain genes escape inactivation, and their overexpression results in phenotypic abnormalities in Klinefelter and Triple X syndromes, while expression of these genes is lower in Turner syndrome due to haploinsufficiency. Klinefelter syndrome exhibits a wide range of clinical presentations, but above-average height is the most common phenotype. They often have small testes and gynecomastia. There is a tendency for learning difficulties, and many show lower verbal intelligence. Turner girls have short stature. Common cardiac abnormalities include coarctation of the aorta and bicuspid aortic valve. Gonadal dysgenesis is common, preventing the onset of puberty. IQ ranges within the normal range, with deficits in visual-spatial abilities. Triple X syndrome rarely causes obvious physical abnormalities. Girls with Triple X syndrome may have slightly lower intelligence and difficulties in verbal skills. Boys with XYY syndrome are usually taller than average and exhibit an IQ 10 points lower than the average. Treatment is mainly symptomatic, with special attention given to the patient's comorbidities and early disease detection. Testosterone replacement therapy is used in Klinefelter syndrome, while estrogen and growth hormone therapy are used in Turner syndrome.