The invention relates to a medical instrument with a shaft, a handle mounted on the proximal end of the shaft, and a tool mounted on the distal end of the shaft and capable of being activated by means of the handle, where the handle and the tool are in active connection by means of at least one activation rod. To make it possible for the tool, in particular as a one-way tool, to be secured simply and rapidly on the activation rod, the invention proposes that the tool should have a tool shaft for securing it to the activation rod and that the tool shaft and the activation rod in order to be secured to one another should have protuberances and/or recesses, which can be engaged, at least partially as a form-locking connection, with corresponding recesses or protuberances of the other respective component.