The rationale of this study was to evaluate the efficacy of Dog-assisted Therapy (DAT) in children and adolescents with Fetal Alcohol Spectrum Disorder (FASD). We conducted a randomized controlled trial in a cohort of 71 children and adolescents with FASD. Participants were randomly assigned either to DAT group (n = 38) or Relaxation Group (control group) (n = 33). Results revealed that participants who were assigned to the DAT group experienced significantly reduced externalizing symptoms (CBCL Externalizing Inattention: t (69) = 2.81, p = 0.007; d = 0.7); CBCL Opposition: t (69) = 2.54, p = 0.013; d = 0.6), reduced internalizing symptoms (CBCL Social problems: t (69) = 3.21, p = 0.002; d = 0.8) as well as improvements on social skills (SSIS-P Problem behavior: t (68) = 2.55, p = 0.013; d = 0.6), and quality of life (KidScreen Autonomy and Parents: t (51) = - 2.03, p = 0.047; d = 0.5) compared to the relaxation control group. The relaxation control group obtained significant differences between the pre- and post-treatment evaluation, diminishing withdraw symptoms (t (32) = 3.03, p = 0.005; d = 0.2). Results suggest that DAT and relaxation may be promising adjunctive treatments for children and adolescents with FASD.