Paratuberculosis is an infectious and incurable disease which causes considerable economic losses in dairy cattle, due mainly to premature disposal and losses of milk production. In 1984 the Animal Health Service North-Netherlands started a vaccination trial in which young calves were vaccinated once, to test whether vaccination reduced the production losses and whether the overall costs of vaccination were outweighed by the benefits. Vaccination against paratuberculosis reduced the number of clinically infected animals by almost 90 per cent. It also reduced the numbers of subclinically infected animals and animals with a positive histological and/or bacteriological test result. Although vaccination did not prevent losses in milk production, it reduced the infection pressure and the clinical signs of the disease. Partial budgeting showed that vaccination against paratuberculosis was highly profitable. The costs of vaccination were US$15 per cow and the benefits (total returns minus costs) were US$142 per cow.