Although ultrasonographic findings of female pelvic mass are frequently reported, those of acute PID are not well established. But, differentiation of fluid collection and mass lesion of PID is exactly made by ultrasonography. We analysed the ultrasonographix findings in 26 cases of acute PID having satisfactory operative or histological proofs, examined at Soonchunhyang Univ. Hospital from Oct. 1985 to Feb. 1987. RESULTS : 1. The age was ranged from 17 years to 53 years of age and the majority was between 21 years and 50 years of age. 2. Ultrasonographic findings are classified to fluid collection in fluid collection in cul de sac 17, tuboovarian abscess 7, pyosalpix 2, endometritis 1 and normal 2 cases. 3. In cases of pelvic mass formation, their ecnogenecity were cystic form in 6 cases, mixed form in 19 cases, solid form in 2 cases, and shapes were mainly ovoid with irregular, ill-defined margin. The location of mass is unilateral in 17 cases, bilateral in 10 cases.