Background:Data from the Avon Longitudinal Study of Parents and Children (ALSPAC) were analysed to investigate associations between parents’ locus of control (LOC) and their use of their children’s symptoms to pursue a diagnosis of autism. Methods:Comparison of parental LOC obtained prenatally with various aspects of the child’s (<12 years) development, used the prevalence of four autistic traits, to ascertain the likelihood that they qualified for an autism diagnosis.Results:Parents with an external LOC had children who were more likely to demonstrate extreme levels of each of the four autistic traits (e.g. for social communication 8.9% of offspring of internal LOC versus 12.3% of external LOC mothers; P<0.0001). However, the rate of autism diagnosis was considerably greater if the mother was internal compared to external (13.3 v 9.6 per 1000). To determine whether the difference was autism specific, we compared parental LOC with children diagnosed with dyslexia and those with reading impairments. Although externals’ children had more reading impairment indicators than internals, this was not reflected by them being more likely to be diagnosed as dyslexic.Conclusions:We conclude that children of parents with an externally oriented LOC may be less likely to be diagnosed appropriately than children of internally oriented parents. Interventions to increase parental internality may improve the likelihood of appropriate diagnoses and hence an improvement in child well-being.