BACKGROUND 47,XYY syndrome is a sex chromosomal abnormality observed in humans, with a prevalence of 0.1% of male births. Sex chromosome anomalies are more frequently associated with male infertility. METHODS We present here four cases of infertile men with azoospermia or severe oligozoospermia attending a genetic and fertility clinic. Chromosomal analysis of the peripheral blood lymphocytes demonstrated the constitutional karyotype of 47, XYY. Using fluorescence in situ hybridization (FISH) the presence of extra Y chromosome was confirmed, supporting the cytogenetic finding. CONCLUSIONS The 47,XYY syndrome is relatively uncommon and can be missed clinically because of its variable clinical presentations. Accurate diagnosis of this constitutional karyotype provides a valuable aid in the counselling and early management of the patients who undertake fertility evaluation.