Rieger syndrome (RS) is an autosomal dominant disorder of morphogenesis characterised by malformation of the anterior segment of the eye, dental hypoplasia, and failure of the periumbilical skin to involute. RS has been mapped to the 4q25-q27 chromosomal segment by a series of cytogenetic studies as well as by genetic linkage to DNA markers. It was first localised to chromosome 4q based on an association with a constitutional deletion of 4q23-q27. In this paper we localise the proximal breakpoint of this deletion from the original patient, and we describe a new family with a de novo balanced reciprocal translocation t(4;12)(q25;q15) segregating with full RS in two generations. Using FISH and the P1 artificial chromosomes (PACs) as probes, we have physically localised both the deletion and the translocation breakpoints between genetic markers which are known to be strongly linked to RS. We have mapped both the proximal deletion breakpoint and the translocation breakpoint within a region between two groups of PACs bearing the markers D4S2945 (on the centromeric side) and D4S193 and D4S2940 (on the telomeric side). We believe that these recombinant bacterial clones derived directly from genomic DNA (not subcloned from YACs) will be valuable complementary tools in the efforts to clone the RS gene and to construct a full transcriptional and sequence ready map of this region.