Recently, Chlamydia trachomatis infection in sexually active women has increased. C. trachomatis cause pelvic inflammation. A few of these patients develop Fitz-Hugh-Curtis syndrome (FHCS). Clinical symptoms of FHCS include pain of sudden onset in the right upper quadrant mimicking acute biliary disease. Diagnosis of FHCS has been weighed upon laparoscopic findings. Since FHCS is a benign disorder which responds to appropriate antibiotics, non-invasive diagnostic method would be expected. We report here two cases of FHCS, diagnosed by a high serum antibody titer against C. trachomatis and clinical manifestations. Both cases showed small effusion in the pelvic cavity detected by ultrasonography, one of them was associated with small effusion in the right perirenal space suggesting perinephritis. Detection of small effusion intra abdominal cavity or pelvic space could be useful for non-invasive diagnosis of FHCS.