Although aneuploidies are common structural chromosomal abnormalities, double aneuploidies involving chromosomes 21 and Y are very rare. Here we report a case of double aneuploidy involving chromosomes 21 and Y in a 5 day old baby with jaundice and polycythemia. The diagnosis was confirmed by karyotype analysis using modified “whole blood” and microtechnique methods followed by Giemsa-Trypsin-Leishman (GTL) banding technique. The patient had typical features of Down syndrome, however, phenotypic features of XYY was not present. In addition, the patient also had atrial septal defect, multiple trabecular small ventricular septal defect, and moderate degree of pulmonary hypertension. Etiological predisposing factor for 48,XYY,+21 is not known. It is difficult to determine the incidence, phenotypic properties, and recurrence risk of 48,XYY,+21.