Maedi-visna virus infection in a flock of sheep in Scotland was associated with respiratory disease, neurological disease, mastitis and lameness. The major clinical signs were dyspnoea (particularly on exercise), progressive fore- and hindlimb ataxia and balance defects, mammary induration and multilimb lameness, occasionally with enlarged carpal joints. Pathological examinations revealed lesions in the lungs, central nervous system, mammary glands and joints which were consistent with those induced by maedi-visna virus. The was no clinical or pathological evidence of concurrent sheep pulmonary adenomatosis, and pulmonary bacterial infections, when they occurred, were superimposed on the lesions due to maedi-visna virus.