Dystrophia myotonica suffers from an obscurity undeserved because, contrary to general impression, the disease is fairly common, frequently unrecognized and of great general medical interest. Of the 13 patients included in this report, 8 were discovered by the purposeful investigation which we made of the families of our patients previously recognized to have the disease. Of the first group of 5 patients presenting themselves at the Colorado General Hospital for treatment, not one heretofore had had his condition correctly diagnosed. All 13 patients came under our observation between 1935 and 1938. Fleischer's1report in 1918, pointing out the hereditary features of the disease, was based on a study of 38 patients seen in the ophthalmic clinic at Tübingen, Germany. Maas2in 1937, from the National Hospital for Nervous Diseases in London, published his investigation of 57 families, among which he found 127 unmistakable cases of the disease and