This paper reviews the current status of preimplantation genetic diagnosis (PGD), outlining the methods currently in use for the diagnosis of sex and single-gene defects. New approaches under development are described, e.g. fluorescent polymerase chain reaction (PCR), the use of sub-telomeric probes for patients with balanced reciprocal translocations, the analysis of first and second polar bodies, the use of lasers to facilitate the biopsy of embryos, and ways forward for infertile patients.