PURPOSE: To classify the hydrosalpinx in the transvaginal ultrasonography for improving the diagnostic accuracy. MATERIALS & METHODS; Among the patients who were diagnosed as hydrosalpinx after surgery from March 1996 to July 1997, 48 patients (51 cases) who were examined with transvaginal ultrasonogram were studied retrospectively. Hydrosalpinx was classified based on its morphology and wall thickeness into the following five types. 1) Type Ia-tortous and connected tubular sonolucent lesion without wall thickening, 2) Type Ib-tortous and connected tubular sonolucent lesion with wall thickening, 3) TypeII-connected tubular sonolucent lesion and the other round sonolucent lesion, 4) Type IIIa-one chambered round or tubular sonolucent lesion, 5) Type IIIb-uni or multi-chambered sonolucent lesion. Each types of lesion was correlated with past operation history and CA 125 level. CA 125 level of 35 U/mL or higher was considered positive. RESULTS: Among 51 cases of hydrosalpinx, which were pathologically confirmed after surgery, type Ia 15 cases, type Ib 3 cases, type II 4cases, type IIIa 11 cases, type IIIb 18 cases. 21 out of the above 51 cases were pre-surgically diagnosed as hydrosalpinx based on TVUS findings were considered of 14 cases of type Ia, 3 cases of type Ib, 2 cases of type II and 2 cases of type III b. Twenty four cases had past operation history and CA 125 level was within the normal range for 28 patients except two patients who has uterine adenomyosis. CONCLUSION: Since transvaginal ultrasonographic findings of hydrosalpinx can be diverse, utilization of such clinical parameters as past operation history and CA 125 level may improve the accuracy of diagnosis.