The CTG trinucleotide repeat (CTG repeat) length in leukocytes and muscles shows significant correlations with muscle weakness, an increase in type 1 fiber proportion, and reductions in type 2A and 2B fiber proportions in patients with myotonic dystrophy (DM). The correlations are generally greater for CTG repeat length in muscles than in leukocytes. However, relatively small absolute values of correlation coefficients (r2 = 0.13-0.43) suggest that the CTG repeat length is not a role variable that may explain clinical and histopathological changes in DM patients.