Background: Subcutaneous Immunotherapy (SCIT) provides long-lasting benefits when administered for 3 to 5 years. Objective: We evaluated SCIT adherence and factors associated with adherence in a military health care system with no out-of-pocket expenses. Methods: We performed a combined retrospective and prospective observational electronic medical record review of SCIT from 2005 to 2012 to determine the start of therapy, time to maintenance dose (MD), duration of MD, and associated factors. Results: We enrolled 897 patients selected for SCIT. A total of 421/897 (47%) were of male sex, 269/897 (30%) had asthma, and 113/897 (13%) had a systemic reaction. Ages ranged from 1 to 74 years (mean 34.8). There were 751/897 (84%) who were on aeroallergen immunotherapy, 108/897 (12%) on imported fire ant immunotherapy, and 54/897 (6%) on venom immunotherapy. Therapy was not initiated in 130/897 (14%) patients. There were 538/897(60%) who received at least 1 MD; 307/897 (34%) completed 3 or more years of MD SCIT, 26% completed 4 or more years of MD SCIT, and 19% completed 5 years or more of MD SCIT. For those reaching MD, the mean total duration was 4.23 years and the mean time on MD was 3.17 years. Men were 271/421 (64%) more likely to reach MD (P = .01). The presence of asthma, age, venom immunotherapy/fire ant immunotherapy vs aeroallergen immunotherapy, and systemic reaction were not associated with reaching MD. After achieving MD, none of the identified factors were associated with SCIT duration. Conclusion: Even with no out-of-pocket expenses, adherence to an adequate course of SCIT was 34%. Only the male sex was significantly associated with reaching MD. No factors were associated with the duration of SCIT after MD.