The study aims to analyze the effectiveness of a swimming program on interpersonal skills, autistic mannerisms, and aquatic abilities in children with autism spectrum disorders (ASD). Research on aquatic therapy showed improvements in motor skills, whereas there is little evidence of effectiveness of this approach on social impairments of ASD. Participants included 25 children, 13 in the experimental group and 12 in the control group, matched for gender, age and autism score. The results showed an advantage in the relational skills for the experimental group at the post-test. The tendency to ameliorate other symptomatology, e.g., autonomy and negative behaviors, persisted at follow-up. Likewise, positive changes in aquatic skills were maintained 6 months after the end of the program.