Preimplantation genetic haplotyping (PGH) proof-of-principle was demonstrated by multiple displacement amplification (MDA) of single buccal cells from a female donor and genotyping using 12 polymorphic markers within the dystrophin gene; the known paternal genotype enabled identification of the paternal haplotype in the MDA products despite 27% allele dropout. MDA amplified DNA from 49 single human blastomeres with 100% success. The MDA products were genotyped using a total of 57 polymorphic markers for chromosomes 1, 7, 13, 18, 21, X and Y; 72% of alleles amplified providing results at 90% of the loci tested. A PGH cycle was carried out for Duchenne muscular dystrophy. One embryo was biopsied: PGH showed a non-carrier female, which was transferred with no resulting pregnancy. A PGH cycle was carried out for cystic fibrosis. Seven embryos were biopsied and PGH allowed the exclusion of 2 affected embryos; a carrier and a non-carrier embryo were transferred resulting in an on-going twin pregnancy. PGH represents a paradigm shift in embryo diagnosis, as one panel of markers can be used for all carriers of the same monogenic disease, bypassing the need for development of mutation-specific tests, and widening the scope and availability of preimplantation genetic testing.