Although time to efficacy of allergen-specific immunotherapy for treatment of canine atopic dermatitis is expected to be slower than with other treatments (eg, antiallergic drugs, biologics), time to clinical efficacy of allergen-specific immunotherapy is unclear. This study reviewed data on 194 dogs from 12 publications to obtain information on efficacy rate and time to efficacy of subcutaneous immunotherapy for treatment of atopic dermatitis. Efficacy was defined as a ≥50% reduction in pruritus and/or skin lesions. Efficacy rate ranged from 65% to 100%, and time to efficacy ranged from 3 to 9 months. Novel allergen-specific immunotherapy regimens resulted in similar to higher efficacy rates and shorter time to efficacy than aqueous and alum-precipitated–based subcutaneous immunotherapy formulations. Because time to efficacy for current aqueous and alum-precipitated regimens is variable, the authors recommend that atopic dogs receiving this type of subcutaneous immunotherapy undergo progress evaluations at least every 3 months.