The gene for myotonic dystrophy (DM), the most common form of adult muscular dystrophy, has previously been mapped to the proximal long arm of chromosome 19. We have conducted linkage analysis on 53 DM families (comprising 421 individuals) using seven DM-linked DNA markers. This analysis, combined with our somatic cell hybrid mapping panel data, places the DM locus more distal on the chromosome 19 long arm than previously thought. Further, we have been able to unequivocally identify DNA markers that flank the disease locus. The definition of a 10-cM region of chromosome 19 that contains the DM locus should prove useful in both the search for the causative gene and the molecular diagnosis of DM.