Introduction: Intrauterine device (IUD) insertion is a painful procedure, particularly for nulliparous women. Interventions to reduce IUD insertion pain have not been identified. Nitrous oxide administered with oxygen (NO) is a safe analgesic with minimal side effects. We compared IUD insertion pain reported by nulliparous women randomized to NO versus oxygen. Objective: 1. To compare mean pain scores measured by a validated visual analog scale (VAS) after IUD insertion in nulliparous women randomized to inhaled NO versus oxygen as placebo. 2. To compare overall patient satisfaction by a five point Likert scale between nulliparous women who are randomized to NO versus oxygen as placebo for IUD insertion. Methods: This double-blinded, randomized controlled trial enrolled nulliparous women ages 13-45 desiring IUD insertion. Women received oxygen or 50/50 NO through a scented nasal mask during IUD insertion. Baseline, anticipated and maximum procedural pain scores on a 100 mm VAS were collected. Satisfaction with pain management was reported on a 5-point Likert scale and a 100 mm VAS. A sample of 40 women per arm was required to determine a clinically significant difference in mean VAS pain scores of 15mm with 80% power and alpha=0.05. Results: Eighty of 93 eligible women were enrolled and randomized. Mean age of participants was 25.6 ± 5.8; 72% were non-Hispanic White and 36% were Hispanic. Mean maximal pain scores at the time of IUD insertion were similar between groups [54 ± 25 mm (NO) vs. 55 ± 21 mm (Oxygen) (p=0.85)]. Linear regression did not change outcomes. Women in the NO group were more likely to be satisfied with their pain management (p=0.04) on the Likert scale but did not have lower VAS scores. Conclusion: NO administration at a ratio of 50:50 did not reduce IUD insertion pain in nulliparous women, however satisfaction with pain management was higher in the NO group.