The objectives were to 1) define the amount of postfracture swelling at presentation in long bone fractures, and 2) to study the relationship between suspected abuse and/or neglect (A/N) and degree of postfracture swelling at presentation. This was a prospective study of 37 patients less than 11 years of age presenting with long bone fractures to the emergency department (ED) of the Children's Hospital of Michigan between August 1992 and December 1992. Data were recorded at the time of the ED visit and from medical records which were reviewed four to six months later. Of the patients enrolled in the study, eight were categorized as A/N and 29 as nonintentional. There was no difference in reported injury age between the two groups (15.5 +/- 24.5 hours vs 14.0 +/- 17.7, P = 0.8). At presentation the mean increase in circumference from post-fracture swelling was 9.6 +/- 7.1%, using the uninjured extremity as the control. The abuse group had a lesser increase in circumference compared to the nonintentional group, even after adjusting for injury age (3.8 +/- 3.6% vs 11.2 +/- 7.0%, P < 0.006). We concluded that patients with long bone fractures had a mean swelling of 9.6 +/- 7.1% at presentation. Injuries induced by A/N present with less swelling than similar injuries sustained nonintentionally, and we speculate that this difference indicates that the history and/or time of injury may not be reliable.