This study tested the "spectrum hypothesis," which posits that children and adolescents with high functioning autism (HFA) differ "quantitatively" but not "qualitatively" from typically developing peers on self-reported temperament. Temperament refers to early-appearing, relatively stable behavioral and emotional tendencies, which relate to maladaptive behaviors across clinical populations. Quantitatively, participants with HFA (N = 104, aged 10-16) self-reported less surgency and more negative affect but did not differ from comparison participants (N = 94, aged 10-16) on effortful control or affiliation. Qualitatively, groups demonstrated comparable reliability of self-reported temperament and associations between temperament and parent-reported behavior problems. These findings support the "spectrum hypothesis," highlighting the utility of self-report temperament measures for understanding individual differences in comorbid behavior problems among children and adolescents with HFA.