Introduction Autism spectrum disorder is a neurodevelopmental condition that exhibits itself in children with impaired communication, sensory and learning problems. It is established that autism spectrum disorder is an inheritable disorder with rates of autism varying with gender in a ratio of approximately four males to every one female. The debate over the genetic causes of autism continues with the variations in autistic phenotype being due to a combination of genetics and a range of environmental factors. Many of the risk factors for autism spectrum disorder occur prenatally and include a plethora of conditions but not limited to the following factors; age of parents, infections, asthma and autoimmune conditions, gestational diabetes, iron deficiency, obesity, anxiety, stress and depression. This review investigates the possible role of excess prenatal cortisol in the development of autism spectrum disorder in children who may be genetically predisposed to the detrimental effects of excess cortisol and appraises many of the reported prenatal risk factors which are either caused by excess cortisol or contribute to elevated cortisol during gestation. Conclusion If cortisol is an environmental contributor to the development of autism spectrum disorder, many of the risk factors (i.e. stress, iron deficiency, uncontrolled asthma) that result in the elevation of cortisol during pregnancy are treatable and as such a greater awareness is required by practitioners to understand that high cortisol levels should raise the same concerns during gestation as does elevated glucose levels.