Nine patients with characteristic changes of Eales' disease in the eye in whom there was neurological involvement, have been described. The characteristic neurological picture comprised an acute or subacute myelopathy occurring at an interval of a few weeks to a few years after the eye episode; in only 1 patient was there cerebral involvement without any evidence of myelopathy. Besides the involvement of spinal cord at the dorsal level in the 8 patients, there was evidence of additional lesions in the brain stem in 1 patient and in the cervical cord in another. The neurological disability was severe, affecting pyramidal and sensory pathways with involvement of sphincters in all 8 patients with myelopathy. There was a tendency to slight improvement in 7 of these and in 4 there was further relapse at the same site. On later examination, the patients exhibited slight to moderate disability and 2 died of chronic renal failure. In the acute or subacute phase of the illness, CSF showed elevation of proteins and cells higher than that seen in patients with multiple sclerosis (MS). Although superficially the clinical symptomatology tended to be similar to MS, there were notable differences from MS in the eye signs, neurological picture and CSF changes. Our observations and the existing literature suggest that the neurological manifestations are likely to be due to an expression of Eales' disease which usually affects only the eyes, with periphlebitis, retinal haemorrhages and neovascular formation. The aetiology of Eales' disease is uncertain but hypersensitivity to a variety of allergens and notably to tuberculosis, needs to be considered.