Since the introduction of computed tomography (CT), there have been numerous reports of brain abscess treated successfully without surgery. Because pathologic confirmation was lacking in these patients, diagnosis was based on CT abnormalities, usually ring enhancement. However, our recent clinical experience and the experimental work of others indicate that the "ring sign" on contrast-enhanced CT is not absolutely diagnostic of encapsulated brain abscess. Moreover, in the reported cases of alleged brain abscess cured medically, atypical clinical features suggest that some patients may have had cerebral infarction or cerebritis. Stricter clinical and radiologic criteria are needed before concluding that encapsulated brain abscess can be cured by medical therapy alone.