Abnormal neurofilament aggregates are pathological hall-mark of most neurodegenerative diseases, although their pathogenic role remains unclear. Increased expression of medium neurofilament (NFM) is an early molecular marker of wobbler mouse, an animal model of motoneuron disease. In the wr/wr, a vacuolar neuronal degeneration (VND) starts at 15 days postnatally, selectively in cervical spinal cord and brain stem motoneurons. Here we show that nfm gene hyperexpression is restricted to the aforementioned motoneurons and is specific for wr mutation. NF proteins accumulate in wr/wr before VND. wr/+ mice, which are asymptomatic, show intermediate NF accumulation between wr/wr and +/+ littermates, suggesting a gene dosage dependence of the wobbler pathology. Altogether our data indicate that NF hyperexpression and regionalized motoneuron degeneration are linked to the wr mutation, although with a still unknown relationship to the mutant gene activity.