Klinefelter's syndrome is generally characterized by hypergonadotrophic hypogonadism and azoospermia. The clinical features, however, are variable, and occasionally severe oligozoospermia may be present. Usually in these cases a 46,XY/47,XXY mosaic karyotype is involved. However, focal spermatogenesis and severe oligozoospermia have been reported in 47,XXY individuals too. In the present study we investigated whether testicular spermatozoa can be recovered in 47,XXY patients with a view to intracytoplasmic sperm injection (ICSI). In four out of nine apparently non-mosaic 47,XXY patients, spermatozoa were recovered from the wet preparations of testicular tissue and ICSI was performed in three couples. In one patient in whom spermatozoa were successfully recovered and used for ICSI, no spermatozoa were retrieved at a second trial. Although these results show that in some 47,XXY individuals testicular spermatozoa can be successfully recovered and even used for ICSI, at present this approach should be considered experimental. There may indeed be some concern about the chromosomal normality of the embryos generated through this infertility treatment. Patients with Klinefelter's syndrome should therefore be counselled about the complexity of this treatment, which involves multiple testicular biopsies from hypogonadal testes, ICSI and preimplantation diagnosis by fluorescence-in-situ hybridization.