Background: An inherited disorder, X-linked adrenoleukodystrophy (X-ALD) is known to cause progressive inflammatory demyelination. Objective: To analyze the adult pattern of disease progression in X-ALD. Design, Setting, and Patients: We retrospectively assessed magnetic resonance (MR) images obtained in adult patients who had developed cerebral disease between January 1, 1985, and December 31, 2005. We identified 103 adult patients with X-ALD with lesions on their MR images. Of these, 56 had serial MR examinations at least 1 year apart and were included in this study. Main Outcome Measure: Progression of X-ALD lesions on MR images. Results: On initial presentation, 17 patients with X-ALD had corticospinal tract lesions without splenium or genu involvement, 24 had symmetric corticospinal tract lesions with additional involvement of the splenium or genu, and 15 did not have corticospinal tract involvement but had other white matter lesions. In 18 of 21 patients with progressive lesions, corticospinal tract involvement preceded or occurred concurrently with progressive inflammatory demyelination. Conclusions: Brain MR imaging abnormalities in adults with X-ALD progress slower than those reported in childhood. The involvement of the corticospinal tracts is prominent and may at times represent a variant course of progressive inflammatory demyelination.