The study of temperament in Autism Spectrum Disorder (ASD) has the potential to provide insight regarding variability in the onset, nature, and course of both core and co-morbid symptoms. The aim of this systematic review was to integrate existing findings concerning temperament in the context of ASD. Searches of Medline, PsychInfo and Scopus databases identified 64 relevant studies. As a group, children and adolescents with ASD appear to be temperamentally different from both typically developing and other clinical non-ASD groups, characterized by higher negative affectivity, lower surgency, and lower effortful control at a higher-order level. Consistent with research on typically developing children, correlational findings and emerging longitudinal evidence suggests that lower effortful control and higher negative affect are associated with increased internalizing and externalizing problems in ASD samples. Longitudinal studies suggest there may be temperamental differences between high familial risk infants who do and do not develop ASD from as early as 6-months of age. Limitations of existing research are highlighted, and possible directions for future research to capitalize on the potential afforded through the study of temperament in relation to ASD are discussed.