Myotonic dystrophy is a progressive neuromuscular disease. Myotonic dystrophy type 1 (DM1), or Steinert's disease, can be classified into four phenotypes: congenital (at birth), childhood-onset (between 1 and 10 years old), adult-onset or classic (10 to 30) and late-onset asymptomatic (20 to 70). Nevertheless, interindividual variability of symptoms even in the four set phenotypes is vast and information on the natural course of disease sparse. The Motor Function Measure (MFM) scale is a standardized quantitative functional examination scale suitable for the whole gravity spectra of neuromuscular diseases including DM1. So far, no percentile curves for the MFM exist for this disease.