Abstract: In this study, tench (Tinca tinca) were caught between March 2003 and February 2004 in Lake Beysehir and examined for Ligula intestinalis plerocercoid infestation. Prevalence ranging from 25.80±2.29-96.88±2.17, increased with increasing fish size. Index of parasitization (Ip) differed among the length classes. Monthly fluctations in Ip values were also significant (p<0.05). Minimum Ip was determined as 1.50±0.26 in April and maximum Ip 4.64±0.60 in January. Mean intensity varied in the length classes. During the studied period, significant differences were observed between mean intensity of plerocercoids values and the months (p<0.05).