Introduction: Incentive spirometry (IS) is commonly used in post-operative patients for respiratory recovery. Literature suggest that it can possibly improve lung function and reduce post-operative pulmonary complication. There is no recommendation about the use of IS in the emergency department (ED). However, rib fractures, a common complaint, increase the risk of pulmonary complications. There is heterogeneous ED practice for the management of rib fractures. The objective of this study is to assess the benefits of IS to reduce potential delayed complications in ED discharged patients with confirmed rib fracture. Methods: This is a prospective observational planned sub-study in 4 canadians ED between November 2006 and May 2012. Non-admitted patients over 16 y.o. with a main complaint of minor thoracic injury and at least one suspected/confirmed rib fracture on radiographs were included. Discharge recommendations of IS use was left to attending physician. IS training was done by ED nurses. Main outcomes were pneumonia, atelectasis and hemothorax within 14 days. Analyses were made with propensity score matching. Results: 450 patients with at least one rib fracture were included. Of these, 182 (40%) received IS with a mean age of 57.0 y.o. Patients with IS seem to have worse condition. 61 (33.5%) had 3 fractures comparatively to 56 (20.9) for patient without IS. Although, the groups were similar for mean age, sex and mechanism of injury. There were in total 76 cases of delayed hemothorax (16.9%), 69 cases of atelectasis (15.3%) and five cases of pneumonia (1.1%). The use of IS was not protector for delayed hemothorax (RR= 0.80, 95% CI [0.45 1.36]) and nor for atelectasis or pneumonia (RR=0.74, 95% CI [0.45 1.36]) Conclusion: Our results suggest that unsupervised and broad incentive spirometry use does not seem to add a protective effect against the development of delayed pulmonary complications after a rib fracture. Further study should be made to assess the usefulness of IS in specific injured population in the ED.