The separation of females and males after mating is a usual practice when the reproductive phase of astacids takes place under controlled conditions and is carried out to avoid egg losses due to male disturbance during spawning and embryonic development. In order to determine the possible effects of male presence on reproductive efficiency, two treatments were tested in the white-clawed crayfish (Austropotamobius pallipes):females alone, and females and males together throughout egg laying and embryonic development, respectively (mean female carapace length = 36.35 ± 0.57 mm). The mating period lasted 19 days. The overall rate of insemination was 98.3%. After 200 days of the experiment, a similar average number of stage-2 juveniles per female was obtained in the two treatments: 48.9± 7.1 in females alone and 46.3± 5.9 with males. In view of the difficulties in separating males and females, and the apparent lack of effect on reproductive efficiency, continued use of the practice should be reconsidered.