Louping ill disease of sheep has been recognised in Scotland for centuries. It causes encephalitis and is transmitted by the sheep tick, Ixodes ricinus. Human infection was first reported in 1934. Thirty-one cases of human infection have now been described. Four clinical syndromes are seen, an influenza-like illness, a bi-phase encephalitis, a poliomyelitis-like illness and a hemorrhagic fever. Certain occupational groups, e.g. laboratory personnel working with the virus and those who kill injected sheep, are at increased risk of acquiring louping ill infection. In many instances, infection is subclinical. Eight new human cases are described. Six were in crofters or shepherds in the north and west of Scotland, one was in a general practitioner in the Western Isles and the eighth was in a butcher in Edinburgh. Louping ill disease should not be forgotten in cases of unexplained encephalitis in those whose lifestyle exposes them to the virus.