This study aimed to evaluate rib fracture rate as well as rib fracture characteristics after thoracic trauma in patients with normal versus diminished bone mineral density (BMD). A retrospective cohort study of persons aged 50 years or older presenting to the Emergency Department after sustaining blunt thoracic trauma between July 1, 2014, and December 31, 2017, was performed. Patient and trauma characteristics and DXA scan results were collected. Rib fracture rate and characteristics were evaluated on a radiograph and/or CT scan of the thorax. In total, 119 patients were included for analysis. Fifty-eight of them (49%) had a diminished BMD. In the remaining 61, the BMD was normal. The diminished BMD group experienced rib fractures more often than the normal BMD group (n = 43 (74%) versus n = 31 (51%);​ p = 0.014). Patients with diminished BMD suffered low-energy trauma more frequently than the normal BMD group (21 (36%) versus 11 patients (15%), respectively (p = 0.011)). Rib fracture characteristics such as the median number of rib fractures, concomitant intrathoracic injury rate, and rib fracture type distribution were not different between the groups. The rate of rib fractures after blunt thoracic trauma was significantly higher in patients with diminished BMD than in patients with a normal BMD. Differences in number and location of rib fractures between groups could not be proven. When assessing patients aged 50 years or older presenting to the hospital after substantial blunt thoracic trauma, the presence of diminished BMD should be taken into account and the presence of rib fractures should be investigated with appropriate diagnostic procedures. Diminished bone mineral density (i.e., osteopenia or osteoporosis) is associated with increased fracture risk. This study evaluated if diminished BMD increases the rib fracture risk. Patients with diminished BMD have a higher risk of sustaining rib fractures after substantial blunt thoracic trauma, which implicates a lower threshold for CT imaging of the chest.