Computed tomography (CT) was the primary diagnostic modality used in the evaluation of 14 patients with 15 surgically proved lesions of the lesser peritoneal sac. CT accurately localized 14 of the 15 abnormalities to the lesser sac. When combined with clinical information, CT correctly suggested the preoperative diagnosis of 13 of 15 lesions. The lesser sac abnormalities included a variety of pathologic entities: pseudocysts, abscesses, hematomas, a perforated gastric ulcer, a biloma, and a malignant neoplasm. The CT anatomy of the normal and abnormal lesser sac is discussed, with emphasis on its various compartments and recesses.