A cutting insert for use in a drilling tool includes two end faces disposed perpendicular to an insert axis and a plurality of side walls connecting the end faces. Supporting surfaces for bearing against corresponding mating supporting surfaces of a cutting insert receptacle of the drilling tool are formed on at least two of the side walls arranged in a rear region of the cutting insert. A main lip for machining a workpiece to be drilled is formed on at least one side wall arranged in a front region of the cutting insert. The side walls having the supporting surfaces are arranged in such a way that the cutting insert can be inserted into a trigon cutting insert receptacle in an accurately fitting manner.