This study assessed how web-based information affects parental trust in physician's diagnosis of autism (PDA) and likelihood of seeking a second opinion. Participants of an online survey were randomly allocated to one of three hypothetical scenarios, all were given a vignette of a non-verbal 18-month-old child followed by (1) not viewing Internet results, (2) viewing results suggesting autism, or (3) viewing results suggesting language delay and rated their trust and likelihood of seeking a second opinion. When Internet results contradicted PDA, parents reported less trust in PDA and greater likelihood of seeking a second opinion. Due to the Internet's influence on parents' response to PDA, clinicians should discuss their differential diagnosis with parents, address Internet-related concerns, and recommend trustworthy sources.