Animal assisted intervention (AAI), which has been defined as the use of an animal to provide therapeutic benefit based on a positive relationship between the client and the animal, is a therapy option for children with autism spectrum disorder (ASD); therefore, it is beneficial to review studies that evaluated its effectiveness. A systematic search identified 20 studies that were assessed in terms of (a) participant characteristics, (b) independent variables, (c) dependent variables, (d) study outcomes, and (e) certainty of evidence. Although AAI studies reported either positive or mixed results, multiple methodological flaws were identified across the literature, which is cause for concern when determining intervention efficacy. Because of these contradictory findings and research design limitations, additional inquiry is needed. As such, caregivers and practitioners should exercise caution in selecting AAI as part of an intervention package for children with ASD.