We studied the occurrence and progression of fatty infiltration, atrophy and edema-like processes in calf and thigh muscles of Myotonic Dystrophy Type 1 (DM1) patients. Fat fraction (FF) and muscle volume (MV) were obtained by a DIXON-sequence and T2 of muscle water (T2water) was calculated by a bi-component extended-phase-graph model. Calf and thigh muscles show fatty infiltration and increased T2water in non-fat infiltrated and fat infiltrated muscles. Atrophy is observed in four calf muscles and one thigh muscles. FF significantly increases in 10 months in fat infiltrated and non-fat infiltrated muscles, but MV only decreases in fat infiltrated thigh muscles.