Merosin, the laminin alpha2 chain located on the surface of muscle fibers, has recently been shown to be absent in a subset of cases with the classical type of congenital muscular dystrophy (Cl-CMD). By immunocytochemistry and immunoblot analysis, using monoclonal antibodies to both the 80- and the 320-kDa fragments, the same protein was found to be only partially deficient in 3 of our cases. All these 3 patients were able to walk, with evidence of a mild to moderate muscle involvement, as opposed to the merosin-negative cases which are never ambulant because they are affected by severe muscular deficit. All of them also suffered from a late onset form of epilepsy, a clinical expression of brain involvement rarely described in cases with merosin-negative CMD. The 3 patients with CMD and partial merosin deficiency were investigated by brain MRI and pattern reversal visual evoked potentials (VEP) associated with electroretinography (ERG). The results were compared with those obtained by similar studies on 3 of our cases with complete merosin deficiency. In both types of patients, the neuroimaging evaluation showed supratentorial white matter changes, usually of moderate degree, irrespective of the amount of merosin detected in muscle. The VEP were normal in all the 3 cases with partial merosin deficiency, whereas they showed reduced amplitude or prolonged latency in all the 3 cases with the merosin-negative form. ERG was normal in all 6 cases. As a whole, our data indicate that leukoencephalopathy does not seem to distinguish between the two variants of Cl-CMD. On the other hand, a benign muscle involvement and normal VEP findings seem to distinguish CMD patients with partial merosin deficiency from those with complete deficiency of the same protein. Late onset epilepsy, evident in all our 3 cases with partial merosin deficiency, needs to be evaluated in a larger series of patients in order to be considered a characteristic of this variant of CMD.