Males of Neptunea arthritica have been shown to mate preferentially with copulated females (CFs) over noncopulated females, which is unexpected due to the increased risk of sperm competition. To investigate how this preference for CFs affects the reproductive success of males, paternity was examined in the offspring of 13 females that had each copulated with three different males following male mate-choice trials. The paternity of each offspring was assigned to its most likely sire using polymorphic microsatellite markers. Males consistently chose CFs. During intromission in the females second and third matings, live sperm cells were detected in the mucus exiting the female shell whereas no sperm were detected during the first matings. In the 13 analysed clutches, single paternity was found in seven clutches, dual paternity was found in three and triple paternity was found in three. These results suggest that males can achieve considerable reproductive success with a mated female through sperm removal.