A rotary pump has a housing composed of two intersecting cylinder sections and pump rotors therein. The rotors roll off on one another and against the interior wall of the housing in a sealing manner and have two approximately club-shaped sections that are connected to each other at their narrower ends via a waisting. The club-shaped section of one rotor engages into the waisting of the other rotor. The rotors create in each phase of the rotation movement an evenly increasing intake volume in front of the inlet port and an evenly decreasing discharge volume in front of the outlet port, provision is made that, in order to improve the pumping performance and increase the stability under load, the surface lines, which function as sealing lines are designed sine shaped.