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To investigate the incidence, severity, and origin of pulmonary fat embolism (PFE) in persons dying from blunt force trauma within 24 hours of injury.The study population consisted of blunt force fatalities. Controls were subjects dying from natural causes or nonblunt force injury. Tissue was removed from lung lobes and prepared for histologic examination using osmium tetroxide to stain for fat. Lung sections were graded for PFE on a scale of 0 (no emboli) to 4 (five or more emboli in a majority of fields).The blunt force group consisted of 56 decedents. Mortality was 93% within 4 hours. Fractures were present in 54 (96%) of decedents, and soft tissue injury was universal. Thirty eight (68%) of decedents were positive for PFE vs. 3 of 20 (15%) in controls. Mean score for PFE was 2.94 ± 1.15 and 1.01 ± 0.94, respectively (p < 0.005). Bone marrow emboli were not observed in any of the sections. Severity of PFE was positively associated with survival time. Analysis of PFE against sex, age, height, weight, number of injuries, and number of fractures showed no significant correlations.A significant degree of PFE develops rapidly in a majority of persons dying of blunt force trauma. Although the source of fat for embolization has been suggested to be bone marrow, no evidence of myeloid tissue was found in any of the lung sections. Nor was there a correlation of PFE and number of fractures. Soft tissue injury is considered the primary cause of PFE.