We estimated the effects of information avoidance and information seeking among parents of children diagnosed with ASD on age of diagnosis. An online survey was completed by 1,815 parents of children with ASD. Children of parents who self-reported that they had preferred "not to know," reported diagnoses around 3 months later than other children. Children of parents who raised concerns that they perceived as having been dealt with adequately reported diagnoses about 4 months earlier, but the children of parents who reported raising concerns repeatedly and felt that those concerns were dealt with inadequately were diagnosed over a year later. These findings suggest that failure of educational and healthcare professionals, in either substituting for parents who avoid information, or supporting those who seek information, can significantly delay the age of diagnosis.