The molecular genetic analyses (PCR and Southern hybridization) of Indian patients with myotonic dystrophy (DM) were carried out to determine the degree of repeat expansion and an attempt was made to correlate the repeat number with disease severity. A scoring system based on the salient clinical features was devised to objectively assess the disease severity. The repeat expansion was seen in 11 of 12 patients examined and showed an inverse correlation with the age of onset confirming the phenomenon of anticipation. This was further established in the two pedigrees studied, clearly demonstrating both clinical and genetic anticipation. The clinical severity score, however, did not correlate well with the repeat number. Nonetheless, such molecular genetic analyses may have immense value as a screening procedure to identify premutations as well as in prenatal diagnoses.