An unusual case of actinomycotic brain abscess with histologic documentation is reported. Commonly, a primary focus of actinomycosis in the cervicofacial, thoracic, or abdominal areas is found. In our particular case such a primary source of infection was not evident. Cranial CT showed a thick-walled ring enhancing lesion deeply located in the left parietal region. This CT finding was useful but not diagnostically pathognomonic. Correct diagnosis was made based on histologic findings. Sulfur granules and Gram-positive branching organisms were seen in the purulent material.