To describe the appearance at ultrasonography (US) of primary epiploic appendagitis in correlation with computed tomographic (CT) findings. From January 1992 through June 1993, clinical, US, and CT findings were reviewed in 14 patients with primary epiploic appendagitis (seven men and seven women, aged 25-51 years [mean, 39 years 3 months]). Follow-up examinations were performed with US alone (n = 4), with US and CT (n = 3), and with clinical examination (n = 14). Surgery was performed in two patients. The main symptoms were right (n = 3) or left (n = 11) flank pain. US revealed an echogenic mass that was small, ovoid, and noncompressible, located anterolateral to the right colon (n = 3), anterior or anterolateral to the left colon (n = 10), and anteromedial to the left colon (n = 1). CT helped confirm the presence of a fatty lesion in each patient without other inflammatory process in the abdomen. Symptoms resolved within 7 days in 12 patients. Primary epiploic appendagitis has fairly characteristic US and CT features that enable a rapid diagnosis.