BACKGROUND: Merosin-deficient congenital muscular dystrophy (CMD) is characterized clinically by hypotonia and muscular weakness and, on imaging studies, by white matter (WM) abnormality. OBJECTIVE: To evaluate MRI findings in Brazilian patients with merosin-deficient CMD. MATERIALS AND METHODS: Twenty-five patients were evaluated using MRI. Three patients presented with partial merosin deficiency and 22 with total merosin deficiency. Follow-up examinations were done in 7 cases. T1- and T2-weighted images were performed in all examinations, and fluid-attenuated inversion recovery (FLAIR) was performed in 15. Enhanced images were done in 11 cases. The WM involvement was classified according to location and severity. RESULTS: From 1991 to 2004, 32 MRI examinations were performed. Severe involvement was found in 23 patients in the frontal and temporal lobes, in 18 patients in the parietal lobes, and in 7 patients in the occipital lobes. The brain stem (n=5), cerebellum (n=6), internal capsules (n=1), and external capsules (n=5) were also affected. One patient had occipital pachygyria, and one had cerebellar vermian hypoplasia. No gadolinium enhancement was noted. Follow-up MRI showed no interval change (n=4), progression (n=1), or improvement of the findings (n=2). CONCLUSION: This series of patients demonstrated that there was no correlation between the extent of WM abnormality on MRI and the clinical status and degree of merosin deficiency (partial or total). Bilateral WM involvement was seen to be more prominent in the parietal, frontal, and temporal regions of the brain. The brain stem and internal and external capsules were less affected. Cerebellar WM involvement is rare. Changes on follow-up imaging studies did not correlate with the clinical status of the patient.