Muscle injuries are, with 6 to 14%, the most common but neglected and under-estimated sport injuries. Certain muscle groups are predisposed to injury depending on the type of sport. There are many hypothesis as to the cause of muscular injury. The prognosis and the length of treatment are greatly influenced by the quality of the first aid administered at the accident site. Simple measures such as compression, elevation, ice and rest can easily be carried out at this site. The further rehabilitation includes bandages and accompanying measures, such as physical therapy and medication. An early functional and conservative therapy is the treatment of choice. The classification of the extent of injury should be carried out by an experienced sportmedic with regard to a differential diagnosis. Sonography and MRI can supply additional information when it is not clear as to the extent of injury. Resulting from an exact as possible classification can the further treatment and planning of the progress of the rehabilitation be established. The necessary length of the pause from sport and of the rehabilitation depend on the seriousness of the injury.