We have previously reported preliminary data on a PKU family showing a discordant segregation of Pvu II (b) alleles at the PAH locus. A combination of several restriction enzymes and probe C2.6 (Intron 2) as well as STR typing were used to dissect the molecular structure of the PAH gene around exon 3. In this family, the results of this analysis and a re-examination of the physical map of the 5'-end of the gene provided strong evidence for the occurrence of a deletion removing exon 3. The "Sicilian" (approximately 2.5 kb) and "Yemenite Jew" (6.7 kb) deletions, the latter one also deleting exon 3, are different in terms of both the 5'-end breakpoint and apparent length. This study, besides adding a new member to the long and increasing list of nearly 200 PAH gene mutations, also proposes to undertake a careful evaluation of RFLP discordances incidentally detected at the PAH locus.