Studies were carried out to evaluate the reproductive efficiency of the narrow-clawed crayfish, Astacus leptodactylus Eschscholtz, 1823, in three different populations in the lakes Apolyont, Iznik, and Manyas in Turkey. Crayfish were sampled monthly using fyke-nets of 34 mm mesh size from April 2002 until March 2003. The average number of pleopodal eggs (with their range), per female, was 200 +/- 12 (8-556) in Lake Apolyont, 202 +/- 13 (6-350) in Lake Iznik, and 257 +/- 13 (18-465) in Lake Manyas. The average number of ovarian eggs (with their range), per female, was 348 +/- 20 (126-630) in Lake Apolyont, 305 +/- 11 (162-465) in Lake Iznik, and 400 +/- 18 (205-776) in Lake Manyas. The average egg diameter and ranges were 2.23 +/- 0.004 (1.80-2.98) mm in Lake Apolyont, 2.53 +/- 0.003 (2.06-2.92) mm in Lake Iznik, and 2.65 +/- 0.027 (1.98-3.04) mm in Lake Manyas. Neither egg diameter nor egg weight increased with body size, but the variability of egg size and weight was high. No relationship was found between egg size and female crayfish size for any of the lakes. Mean size at maturity of female A. leptodactylus varied among the lakes. Females in Apolyont populations reached sexual maturity at a size of 64.3 mm TL, but spawning occurred only when females attained 82-128 mm TL, indicating that the mean minimum reproductive size was 82 mm TL in Lake Apolyont. Average female size was 88.7 mm (+/-SD 0.6; max. 142 mm; min. 48 mm; n = 154). In Iznik Lake, size at maturity of females was 78 mm TL, while spawning size was 83142 mm TL; average female size was 90.6 mm (+/-SD 0.5; max. 139 mm; min. 66 mm; n = 99). Finally, female size at maturity was 72.6 mm TL, and spawning size was 80-130 mm TL in Manyas Lake; average female size was 89.0 mm (+/-SD 1.1; max. 141 mm; min. 29 mm; n = 122). The total observed sex ratio (male/female) was found to be 1.00/0.53 in all three lakes together. Mature A. leptodactylus reproduce only once a year under natural conditions. No evidence was found in this study to suggest the occurrence of multiple spawnings.