This chapter examines the empirical evidence on the mental health impact of the Chernobyl accident. It describes the synopsis of the events of 1986 and discusses the historical and research contexts in which the subsequent mental health studies took place. The chapter reviews three areas of research on the mental health consequences of Chernobyl: stress effects in the general population; cognitive and emotional effects in highly exposed infants; and the cognitive and emotional effects in cleanup workers. Research on the mental health of cleanup workers has focused on the associations of high levels of radiation exposure with subsequent cognitive impairment, neuropsychological dysfunction, and psychosis and rates of emotional problems, including suicide, in general samples of cleanup workers. The mental health impact of Chernobyl on the cleanup workers needs greater study, but the findings to date indicate that highly exposed cleanup workers constitute a high-risk group for psychiatric disorders, especially depression.