In 1998, a novel paramyxovirus (order Mononegavirales, family Paramyxoviridae, subfamily Paramyxovirinae, genus Henipavirus) emerged in peninsular Malaysia causing fatal encephalitis in humans and severe respiratory illness with encephalitis in pigs. The virus was successfully isolated in cultured mammalian cells. Transmission electron microscopy of infected tissue culture cells played a crucial role in the early preliminary identification of the causative agent of the outbreak. This in turn was pivotal to determine the correct direction of control measures that subsequently brought the epidemic under control. In light of this investigation, and indeed identification of infectious agents associated with other disease episodes, electron microscopy will remain an important frontline method for rapid diagnostic virology and investigation of any future outbreak of new and unusual cases of illness suspected of an infectious aetiology.