BACKGROUND AND PURPOSE To describe the long-term follow-up of a cohort of 22 patients with the Miyoshi phenotype of distal muscular dystrophy (MMD). METHODS A long-term clinical follow-up study was conducted. Patients were genotyped for dysferlin (MMD1) or anoctamin 5 (MMD3) mutations. Patients also underwent cardiological evaluation. RESULTS There were 10 patients with MMD1, eight patients with MMD3 and four patients with linkage to chromosome 10 (MMD2). All patients deteriorated over 5.7 (range: 4.2-6.6) years of follow-up. Weakness increased significantly (P < 0.035) in all but the neck extensor, serratus anterior, and wrist flexor and extensor muscles. The decrease of strength was most pronounced in the iliopsoas (15%), toe extensors (15%), anterior tibial and peroneal muscles (10%). Patients with MMD1 showed early onset of the disease (mean 22 years) with typically symmetrical distribution of weakness starting in the calf muscles. Patients with MMD1 had a worse clinical course compared with patients with MMD3. Ninety percent of the former had to make use of a wheelchair within 15 years after onset of the disease, whereas patients with MMD3, who have a significantly later onset (mean 35 years) of asymmetrical calf muscle weakness and atrophy, remained ambulant during the first 15 years of their disease. None of the patients with MMD2 became fully confined to the wheelchair. None of the 22 MMD phenotype patients had heart disease. CONCLUSIONS Patients with MMD1 have a worse clinical course compared with patients with MMD3. There are no cardiological abnormalities in all MMD categories.