A centrifugal blood pump without a mechanical bearing comprises a pump casing (1), an impeller (9) arranged in the pump casing rotatably about the central axis and freely movable axially and radially within a limited clearance. The impeller has permanent magnets or permanently magnetized magnetic regions (N/S) which cooperate with an electromagnetic drive to set the impeller rotating. A circular wall (12) or circularly arranged wall sections are provided within the pump casing, their inner surfaces defining a radial clearance together with the outer circumference of the impeller to form a hydrodynamic radial bearing for the impeller.
