Autism Spectrum Disorders (ASD) are associated with higher levels of anxiety for parents [1]. Provide medical information about autism etiology is the first step to help parents to understand the child disorder and to cope with it. The medical current community accepts that autism is a neurodevelopmental disorder in which genes play a role but that environmental factors likely contribute as well [2]. This conception can meet parent's beliefs constructed on their cultural values and personal experiences. In line with causal attribution theory [3], it is important to consider to parental beliefs because it can impact the treatment choices and the child developmental trajectory [4]. The Main purpose is to evaluate the consistency between parental knowledge and beliefs about ASD etiology. The second purpose is to explore the impact of consistency on parents’ anxiety. We interviewed through open-ended questions 89 parents of ASD children aged between 3 to 10 years about their knowledge and their beliefs about ASD etiology. A content analysis was performed using the Nvivo10 software. Anxiety is evaluated with the subscale of the Hospital Anxiety and Depression Scale (HADS). In agreement with previous work four categories of causes have been identified: biological (BIO), psychological (PSY), multifactorial etiology (BIO + PSY), others (OT). A percentage of 55.1% of parents is consistent between their knowledge and beliefs about ASD etiology while 43.8% are inconsistent. Parent anxiety is significantly higher (T (71.91) = 2.34; P < 0.05) when knowledge and beliefs are inconsistent than when they are consistent. This study demonstrates the deleterious impact of inconsistency between knowledge and beliefs about ASD etiology, on parental anxiety. In order to provide relevant support for parents, information delivered after diagnosis must consider pre-existing parental beliefs. A systematic assessment of parental beliefs would adjust the information provided after the diagnosis.