Background: The concept of the "broad phenotype" of autism refers to the finding that relatives of people with autism often have mild forms of autistic-like characteristics, such as social and communicative difficulties. This study used the Autism Spectrum Quotient (AQ), a questionnaire devised to assess features of the broad phenotype in adults, with parents of people with autism, to see whether they would be more likely to obtain extreme scores than a control group. Methods: The AQ was administered to parents of 69 people with an autism spectrum disorder and parents of 52 controls. Results: On two of the five subscales of the AQ, social skills and communication, parents of people with autism obtained higher scores than control parents. The other three scales, attention to detail, attention switching, and imagination, did not differentiate groups. The correlation between social skills and communication scales was 0.663. The scales can be combined to give an index of broad phenotype. Conclusions: The AQ appears to be sensitive to the broad phenotype, provided attention is restricted to the social skills and communication scales.