Background. Autism spectrum disorders (ASD) are syndromes that are predominantly defined by behavioral features such as impaired social interactions, restricted verbal and nonverbal communication, and repetitive or stereotyped behavior. In the past few decades, the reported prevalence of ASD has increased dramatically. This growth can be partially explained by an increased level of awareness of the problem among professionals and better diagnostic methods. Nevertheless, underpinning causes of ASD have not yet been detailed and explained. It is suggested that rather than having a single causative factor, ASD pathogenesis is influenced by environmental or genetic factors, or a combination of both. The aims of this review are to describe the environmental risk factors associated with ASD so as to provide a reference basis for current and future clinical and experimental work. Materials and methods. On the basis of a PubMed search, we review the existing knowledge on environmental factors associated with ASD. Results. A series of environmental factors have been repeatedly reported as risk factors for ASD in existing studies. Conclusion. Air pollution, organic toxicants, seasonal factors, psychological stress, migration, birth order, and nutrition may have a close relationship with the incidence of ASD.