Twenty cases of clinically patent fat embolism syndrome (FES) were observed at the authors' institution between 1964 and 1989. There were 4 deaths (20%). The injury severity score (ISS) was computed for each patient upon admission and ranged from 9 to 50 (median, 17). The ISS was significantly higher in the 4 deceased patients (P = .014). The incidence of FES amounted to 0.26% of all patients hospitalized with at-risk fractures (femoral and tibial shaft fractures and pelvic fractures). The findings of the 25-year study indicate the following: (1) clinically patent postfracture FES is rare; (2) FES is significantly more frequent in patients with several at-risk fractures than in those with one at-risk fracture (P < .0003); and (3) prognosis appears to be more directly related to ISS than to FES itself.