The population structure of Mesobuthus gibbosus was studied over 261 night-hours of sampling during 29 consecutive nights on Koufonisi Island (central Aegean Archipelago, Greece) using the capture-recapture method. The studied population proved to be the densest of all studied scorpion populations in chaparral or intertidal habitats of Mediterranean type ecosystems and even comparable to some populations of desert scorpion species. The negative influence of moon phase on the general activity of the species and synchronization in parturition were the main factors that caused the fluctuations in population density and therefore in the percentage of active scorpions.