The use of epinephrine for anaphylaxis to subcutaneous allergen immunotherapy (SCIT) is the standard of care, but its use for mild systemic reactions (SRs) is somewhat controversial. The objective of this study is to determine the rate of SR to SCIT, the symptoms reported, and the response to intramuscular (i.m.) epinephrine over a 1 year period. This retrospective study was designed to evaluate SRs to SCIT to any combination of approximately 20 allergens (pollens, animal emanations, molds, and Hymenoptera) in 773 subjects representing 14,707 visits, receiving approximately 28,000 injections over 1 year. Nurses were instructed to administer epinephrine (1:1000 v/v) 0.2 mL i.m. for signs or symptoms of a SR. SRs were graded using the universal grading system proposed by the World Allergy Organization (WAO) Joint Task Force for Grading SR to Immunotherapy. Thirty-one patients (4%) had 32 SRs, 22 (71%) female, average age 40 yr. Nineteen (61%) had a history of asthma; 7 (22.6%) had a history of a previous SR. SRs were reported on average 24 minutes after injection. Symptoms included: generalized pruritus, 34.4%; upper airway pruritus, 28.1%; cough, 25.0%; shortness of breath, 21.9%. Fourteen SRs were classified as Grade 1, thirteen Grade 2, two Grade 3, and three Grade 4. No Grade 5 or late phase reactions were reported. 29 (90.6%) reactions were treated with epinephrine, 27 (84.4%) glucocorticosteroid, and 30 (93.8%) H1 antihistamine. SRs occurred in 4% of patients receiving SCIT and all who received early intervention with epinephrine responded successfully. The WAO Grading system was useful.