A medical cutting instrument for cutting muscles and tendons, with an instrument body that includes a handle on its proximal end and at least one cutting knife in the area of its distal end. To provide a medical cutting instrument that guarantees ease of handling and simple structure along with secure cutting of the muscle/tendon tissue, the instrument body should be of grooved configuration in the area of its cutting knife in such a way that the instrument body includes a hollow space extending in the longitudinal direction of the instrument body to receive and guide the muscle/tendon tissue that is to be cut, such that the instrument body includes an opening extending in the longitudinal direction of the instrument body and the cutting knife constitutes a side of the instrument body.
