Monthly variations and the effects of host size on parasite prevalence and mean intensity were examined in common carp (Cyprinus carpio L., 1758) from Beysehir Lake in Turkey. This study was carried out between March 2003 and February 2005, A total of 233 fish were examined. Three parasites species were identified: Dactylogyrus minutus, Caryophyllaeus laticeps, Bothriocephalus acheilognathi. Infection with Dactylogyrus minutus was recorded on fish in all months with the exception of April. Peak infection occurred in May (69.23%). Infection of C. Caryophyllaeus laticeps was the highest in April (72.22%). Prevalence levels of Bothriocephalus acheilognathi were rather low, less than 35% in all months. The distribution of infrapopulations of Dactylogyrus minutus, Caryophyllaeus laticeps and Bothriocephalus acheilognathi did not vary significantly with size class of fish (P>0.05), peaking in larger size classes.