We examined the error-related negativity (ERN) as an endophenotype of ASD by comparing the ERN in families of ASD probands to control families. We hypothesized that ASD probands and families would display reduced-amplitude ERN relative to controls. Participants included 148 individuals within 39 families consisting of a mother, father, sibling, and proband. Robust ANOVAs revealed non-significant differences in ERN amplitude and behavioral performance among ASD probands relative to control youth. In subsequent multiple regression analyses group and kinship (proband, sibling, mother, father) did not significantly predict ?ERN (error minus correct ERN) or behavioral performance. Results do not provide evidence for the ERN as an endophenotype of ASD. Future research is needed to examine state- or trait-related factors influencing ERN amplitudes in ASD.