Progress has been slow in identifying pre- and post-natal environmental exposures that might trigger the features that characterize autism. During the past thirty years, research in the field of autism has been conducted in a setting in which diagnostic criteria for this condition have changed and broadened, and differences of opinion regarding diagnostic issues and diagnostic terminology continue. The documented prevalence of all forms of autism has increased steadily during this time, suggesting one or more environmental contributors. Not established, however, is whether an increasing incidence of autism is responsible for increasing prevalence. The increase in documented prevalence could result from expanding and changing case definitions and increased reporting due to increased awareness on the part of professionals who work with children and by the public. This review provides a background for the evolving story of autism and describes the research on the relation between autism and the environment, with a particular focus on some of the more recently proposed environmental triggers. Critical analysis of this body of scientific research in a historical framework helps to explain the often controversial nature of the proposed relations between autism and environmental factors, as well as to rationalize some of the pitfalls in research design and in the often questionable interpretation of data so obtained.