This article describes the investigation of a neonatal calf diarrhoea outbreak in a dedicated tuberculosis isolation unit. Like many calf rearers purchasing young calves, this farmer did not have control over the first 7 days of their lives. Focus therefore was on treatment of sick animals, reducing the risk of spread of pathogens and diagnostic testing to aid management. Longer term an all-in all-out programme followed by disinfection, and a review of purchasing policy to help selection of source farms was established.