Autism spectrum disorders (ASDs) affect approximately 1 in 110 children in the United States. This report profiles fetal-brain reactive autoantibodies of a large cohort of mothers of children with autism and controls, yielding significant associations between the presence of IgG reactivity to fetal brain proteins at 37 and 73 kDa and a childhood diagnosis of full autism (p = 0.0005), which also correlated with lower expressive language scores (p = 0.005). Additionally, we report on reactivity to proteins at 39 and 73 kDa, which correlated with the broader diagnosis of ASD (p = 0.0007) and increased irritability on the Aberrant Behavioral Checklist (p = 0.05). This study provides evidence of multiple patterns of reactivity to fetal brain proteins by maternal antibodies associated with ASD and specific childhood behavioral outcomes.