The invention relates to a piston pump (10) with a piston (20) axially displaceable in a bush (12). In order to keep the piston (20) captive in the bush (12), the invention proposes that an annular loss-prevention means (90), with conically protruding spring tongues (96), be inserted in the manner of a snap connection into a V-shaped groove (80) in the bush (12), whose spring tongues (96) resiliently press a groove side (98) of a groove (34) made in the piston (40) into the groove (34), engaging it from behind, when the piston (20) is introduced into the bush (12). (FIG. 1)