The aim of this study was to examine how severity of autism affects children's interactions (relatedness) and relationships with their parents. Participants were 25 parent-child dyads that included offspring who were children with autism aged from 4 to 14 years. The severity of the children's autism was assessed using the calibrated severity metric of the Autism Diagnostic Observation Schedule (Gotham et al. in "J Autism Dev Disord: 39:693-705, 2009). Parent-child dyads were videotaped in 10-min semi-structured play interactions, and qualities of interpersonal relatedness were rated with the Dyadic Coding Scales (Humber and Moss in "Am J Orthopsychiatr" 75(1):128-141, 2005). Quality of relationships between parents and children were evaluated with a parent self-report measure, the Parent Child Relationship Inventory (Gerard in "Parent-Child Relationship Inventory (PCRI) manual." WPS, Los Angeles, 1994). Multivariate regression analysis revealed that severity of autism was inversely related to patterns of parent-child interaction but not to reported quality of parent-child relationship. We consider the implications for thinking about relatedness and relationships among children with autism, and opportunities for intervention.