OBJECTIVE: The authors applied maximum external decompression for malignant hemispheric infarction and investigated the functional outcome according to the patient age. METHODS: Twenty-five patients with malignant hemispheric infarction were treated using a hemicraniectomy with maximum external decompression, comprising a larger (>14cm) hemicraniectomy, resection of the temporalis muscle and its fascia, spaciously expansive duraplasty, and approximation of the skin flap. The medical and diagnostic imaging records for the patients were reviewed, and 1-year functional outcome data obtained for the younger group (aged ≤ 60 years) and elderly group (aged > 60 years). RESULTS: The patients (n=25) who underwent maximum surgical decompression revealed a minimal mortality rate (n=2, 8.0%). The patients (n=14) in the younger group all survived with mRS scores of 2 (n=1, 7.1%), 3 (n=7, 50.0%), 4 (n=3, 21.4%), or 5 (n=3, 21.4%). A majority of the younger patients (57.1% with mRS ≤3) lived with functional independence. When the 1-year mRS scores were dichotomized between favorable (mRS ≤3) and unfavorable (mRS ≥4) outcomes, the younger group had significantly more patients with a favorable outcome than the elderly group (57.1% versus 9.1%, p=0.033). In contrast, in the elderly group, most patients showed unfavorable outcomes with the mRS scores of 4 (n=5, 45.5%), 5 (n=3, 27.3%), or 6 (n=2, 18.2%), whereas only one patient showed favorable outcome (mRS 3). A majority of the elderly patients (45.5% with mRS 4) survived with moderately severe disability. CONCLUSION: For malignant hemispheric infarction, a hemicraniectomy with maximum external decompression was found to considerably increase survival with a favorable outcome in functional independence (mRS ≤3) for younger patients aged ≤60 years. It can be optimal surgical treatment for younger patients.