Different mutations of the phenylalanine hydroxylase (PAH) gene leading to phenylketonuria (PKU) have been described associated with specific haplotypes in several European countries. In order to investigate the distribution of DNA haplotypes in Italy, restriction fragment length polymorphism (RFLP) analysis of the PAH gene was performed in nine Italian PKU patients from eight unrelated families, and in the available relatives. The analysis of eight polymorphic sites revealed haplotypes 1 and 6 in association with PKU. This pattern appears to differ from those reported for other European populations. The majority of the 14 PKU subjects studied showed compound heterozygosity for different haplotypes, as observed for other European series. RFLP analysis at the PAH locus allowed us to offer the possibility of prenatal diagnosis to six of the studied families. One prenatal diagnosis was performed and a normal fetus was diagnosed.