From September 1997 to June 1998 helminth parasites of flounder (Platichthys flesus L.) were studied in Dalyan Lagoon. A total of 45 flounder were caught. From 40 of 45 fish examined only two species of helminth parasites, Ligula intestinalis (Cestoda) and Cucullanellus minutus (Nematoda). The dominant parasite species C. minutus was 89%. This species was the most prevalent. found in fish and the infection was the highest in March. C. minutus was found in 40 of 45 fish examined. Forty fish containing a total of 416 parasites were found. L. intestinalis was found in 9 of the 15 fish examined. Nine fish containing a total of 33 parasites were found. Total prevalence of L. intestinalis was 20%.