A government report concluded that the cause of the recent cluster of illness affecting 57 people at Melbourne Airport was a "mystery". On reviewing the evidence, I noted the appearance of a constellation of distinct psychogenic features (in the absence of an identifiable pathogenic agent or source), and non-specific symptoms not correlated with any particular illness, strongly suggesting a diagnosis of mass psychogenic illness. Given the time differential between the illness onset in the index case and the initiation of air sampling, and the added factor of the air-conditioning in the terminal being switched to exhaust mode, the possibility that a toxic agent was responsible for making some of the victims ill cannot be completely excluded. Future investigations of similar incidents should, in the absence of clinical or laboratory findings, consider the diagnosis of mass psychogenic illness. Failure to do so can engender avoidable confusion and un-ease among the Australian public. The issue of diagnosing collective psychogenic illness will continue to be a major public health challenge, exacerbated by widespread anxieties over the threat of chemical and biological weapons and fears of contamination.