Background Rib fractures are common in ageing people after trauma and delirium is a complication often seen in acutely hospitalized elderly patients. For both conditions, elderly have an increased risk for institutionalization, morbidity, and mortality. This study is the first to investigate risk factors of delirium in elderly patients with rib fractures after trauma. Methods A retrospective chart review was performed on patients ≥65 years admitted with rib fractures after blunt chest wall trauma to the Amphia hospital Breda, the Netherlands, between July 2013 and June 2018. Baseline patient, trauma- and treatment-related characteristics were identified. The main objectives were identification of risk factors of delirium and investigation of the effect of delirium on outcomes after rib fractures. Outcomes were additional complications, length of hospital stay, need for institutionalization and mortality within six months. Results Forty-seven (24.6%) of 191 patients developed a delirium. Independent risk factors for delirium were increased age, physical impairment (lower KATZ-ADL score), nutritional impairment (higher SNAQ score) and the need for a urinary catheter, with odds ratios of 1.07, 0.78, 1.53 and 8.53 respectively. Overall, more complications were observed in patients with delirium. Median ICU and hospital length of stay were 4 and 7 days respectively, of which the latter was significantly longer for delirious patients ( p < 0.001). Significantly more patients with delirium were discharged to a nursing home or rehabilitation institution ( p < 0.001). The 6-month mortality in delirious patients was nearly twice as high as in non-delirious patients; however, differences did not reach statistical significance. Conclusion Delirium in elderly patients with rib fractures is a serious and common complication, with a longer hospital stay and a higher risk of institutionalization as a consequence. Increased awareness for delirium is imperative, most importantly in older patients, in physically or nutritionally impaired patients and in patients in need of a urinary catheter.