Karyotypic abnormalities involving the Y chromosome are common. The clinical spectrum associated with Y chromosome trisomy, tetrasomy or pentasomy is imprecise, as still very few cases have been reported. All cases, however, seem to exhibit some degree of mental retardation and minor facial dysmorphisms. The case we describe is only the fifth reported case of non-mosaic Y tetrasomy. This report and follow-up of a patient, between 4 months and 26 years of age, will certainly be helpful in better characterizing this karyotypic defect.