Actinomycosis is an unusual bacterial infection that most often affects the head and neck region. Abscesses occasionally associated with a draining sinus may result secondary to extensive tissue destruction. We report the CT appearance in a case of actinomycosis of the neck. A thick walled enhancing mass with a low attenuation center was identified between the sternocleidomastoid muscle and the strap muscles of the neck. Enhancement of the adjacent muscles was present. Surgery confirmed an abscess with inflammation of the adjacent muscle. Histologic examination of the specimen showed the presence of multiple yellow (sulfur) granules containing Actinomyces. Computed tomography correctly determined the extent of the mass and lack of involvement of the deep structures of the neck.