A chromosomal survey using the G-banding technique was performed on 87 subfertile male whose semen analysis demonstrated severe oligospermia and azoospermia at Yokohama City University Hospital between January 1990 and October 2002. Fourteen of these subjects demonstrated major chromosomal anomalies (16.1%). Semen analysis in these cases demonstrated azoospermia, except in one case of autosomal abnormality. Twelve patients showed sex chromosomal abnormalities including 8 Klinefelter syndrome (47XXY) and 2 XX males (46XX) and two patients had autosomal abnormalities. The follicle-stimulating hormone (FSH) value in these patients, except for the two cases of autosomal abnormality and one case of 46XYq-, was much higher than normal. Histological examination was performed in 7 cases. In these cases, intratesticular spermatozoa were seen in only two cases (Klinefelter syndrome case and ring chromosome 21 case). Chromosome studies are important in the evaluation of subfertile patients with azoospermia and severe oligospermia. Because the abnormal genotype could be transferred to the next generation, the importance of chromosome studies before ICSI should be emphasized.