Autism spectrum disorders (ASDs) are complex and heterogeneous with a spectrum of diverse symptoms. Current estimates suggest that ASD affects approximately 1% of children and is a major public health issue. Despite decades of research, little is known about factors that contribute to the pathogenesis of the disorder, although both genetic and environmental factors have been implicated. A number of published findings have identified numerous immune abnormalities in subjects with ASD and their families, both at the systemic and cellular levels. In addition, genetic studies have also uncovered a number of candidate genes that link immune function with ASD. Collectively these findings point to a pivotal role for immune-dysregulation in the pathogenesis of ASD. A better understanding of the involvement of the immune response on early brain development and how this is altered in ASD will have important therapeutic implications.