Q fever was first described in Australia and has since been reported from many countries. Rickettsia burneti infects numerous species of mammals and has been isolated from ticks. Infected cattle, sheep and goats remain healthy but excrete the organism, which is present in high concentration in products of conception and survives in dust for long periods. The ways in which humans may become infected are considered. Many of these infections do not cause symptoms, but some are fatal and the prevention of this disease remains a challenge.