The computed tomographic (CT), clinical, and pathologic findings in 9 patients with biopsy-proven herpes simplex encephalitis (HSE) were reviewed. Seventeen scans (5 plain, 12 contrast enhanced) were analyzed. The major CT finding was a low-absorption abnormality, present in 11 of 17 scans (64%), affecting primarily the temporal lobes. Mass effect was evident in 9 of 17 (52%). Of the 12 contrast-enhanced scans, 6 (50%) showed an abnormal enhancement pattern affecting primarily the sylvian fissure and opercular areas. CT abnormalities are characteristic enough that, in the proper clinical setting, they lend support to the correct diagnosis.