PGD has now been practised for a decade. The basic techniques currently used involve embryo biopsy, polymerase chain reaction (PCR) and fluorescent in situ hybridization (FISH). Recent advances in molecular diagnostic techniques have included the use of fluorescent PCR, multiplex PCR and whole genome amplification. For cytogenetic analysis, many centres are now using five or more chromosome probes to examine for chromosome abnormalities, sexing and aneuploidy. Future improvements in molecular diagnosis include the use of quantitative PCR, DNA fingerprinting and microarray technology. Developments in methods to analyse chromosomes from a single cell have included interphase chromosome conversion, which has already been clinically applied, and the use of comparative genomic hybridization, which is still being developed. These methods will hopefully enable more accurate and a greater number of diseases to be diagnosed at the single cell level.