A neurological syndrome in a herd of Friesland cows (n = 100) on a diet including sorghum beer residues is described. Over a period of 8 months, 76 cows developed weakness of the hindquarters, progressively worsening ataxia and, eventually, paralysis and permanent recumbency. The course of the disease varied from 2 to 8 weeks. The lesions were significant in the 2 cows necropsied and included extensive, bilaterally symmetrical dilation of myelin sheaths, axonal swelling and loss with Wallerian degeneration, and depletion of myelin in both ascending and descending tracts at all levels of the spinal cord. Focal neuronal degeneration in the spinal cord grey matter and dorsal root ganglia, and focal loss of axons and ovoid formation in the spinal nerve roots and ischiatic nerves were also evident. The pathogenesis of the spinal lesions appears to involve a primary axonopathy with secondary myelin loss. The epidemiology, clinical signs and pathology suggest that the disease was associated with the fungus Aspergillus clavatus.