We report prenatal diagnosis of phenylketonuria by linkage analysis of the markers linked to the phenylalanine hydroxylase (PAH) gene. Three markers comprising STR (TCTAT)n in intron 3, VNTR (30bp long cassette) in the 3' UTR and Xmn1 RFLP were ascertained in the affected child, the parents and the chorionic villi sample. The foetus was confirmed to be heterozygous for the mutant allele. The diagnosis that the foetus was unaffected was confirmed by biochemical tests in the newborn.