Computed tomography (CT) is valuable in providing a specific diagnosis of abdominal abscess and in determining its site and extent. Computed tomography is also capable of excluding an abscess with a high degree of certainty. In 31 of 34 patients with proven abdominal abscess, CT suggested the correct diagnosis and accurately defined the extent of involvement. In nine patients, the CT findings were specific for abscess. The CT appearance of abscess is diverse, largely depending on its location. The most common appearance is a low density mass often with higher density at the periphery. The presence of gas distributed within the mass or an extraalimentary air-fluid level allows an extremely confident diagnosis of abscess. Differential diagnostic possibilities are reviewed with emphasis on interpretive problems. © 1978 Raven Press, New York.