There is increasing evidence to suggest that dogs are beneficial for children with Autism Spectrum Disorder (ASD) in therapy sessions, and anecdotal reports suggest that dogs may have wider benefits, in a family setting. This study investigated the effect of dog ownership on family functioning and child anxiety. Using a validated scale of family strengths and weaknesses (Brief Version of the Family Assessment Measure-III [General Scale]), we compared parents of children with ASD who had recently acquired a pet dog (n = 42, Intervention group) with a similar group of parents not acquiring a dog (n = 28, Control group) at matched time points. A sub-population (n =14 acquiring a dog, n = 26 controls) completed a parental-report measure of child anxiety (Spence Children's Anxiety Scale). The primary carer completed the scales via telephone at Baseline (up to 17 weeks before acquiring a dog), Postintervention (3-10 weeks after acquisition), and Follow-up (25-40 weeks after acquisition). Over time, scores for family functioning showed significant improvements (reduced family weaknesses, increased strengths) in the dog-owning compared with the non-dog owning group. In comparison with the non-dog owning group, anxiety scores in the dog-owning group reduced by a greater percentage, most notably in the domains of Obsessive Compulsive Disorder (26% greater decrease), Panic Attack and Agoraphobia (24%), Social Phobia (22%), and Separation Anxiety (22%). The results illustrate the potential of pet dogs to improve whole family functioning and child anxiety.