Objective: To determine the clinical course and outcome in patients with a middle cerebral artery (MCA) occlusion and early computed tomographic (CT) scan findings of infarction, particularly relative to age of the patient. Material and Methods: The clinical and neuroimaging features of 42 consecutive patients with MCA occlusion and early CT signs of swelling (within 24 hours after ictus) were studied. CT scans were graded for displacement of the pineal gland and septum pellucidum as well as compression of the frontal horn of the ventricular system. Young adults, defined as younger than 45 years of age, were assessed separately. Results: Overall mortality was 55% in this patient population at risk for further neurologic deterioration. Of the 42 patients, 33 had deterioration-an impaired level of consciousness ensued in 3, a diencephalic herniation syndrome developed in 19, and uncal herniation occurred in 11. Mortality was 70% in these patients with deterioration. Mortality was significantly lower in younger patients with deterioration in comparison with older patients (3 of 11 patients versus 20 of 22; P = 0.00018, Fisher's exact test). Factors predictive of deterioration and poor outcome were older age (more than 45 years) and the presence of hyperdense clot in the MCA on CT scan, in addition to early swelling. Conclusion: Deterioration from further brain swelling is common in patients with MCA occlusion and sulci effacement on early CT scan. The outcome is fatal in most patients who deteriorate. Mortality was significantly higher in deteriorating older patients than in younger patients. Clearly defined criteria for decompressive hemicraniotomy in young patients with complete MCA occlusion are needed, preferably derived from a randomized clinical trial.