Several clinical series, analyzing fracture healing in patients with diabetes mellitus (DM). demonstrated significant incidence of delayed union, non-union, and pseudarthrosis. In this study, analysis was performed to evaluate the effects of blood glucose (BG) control on fracture healing in the DM BB Wistar rat, a rat strain that represents a close homology to Type I DM in man. Our study showed decreased cell proliferation at the fracture site as well as decreased mechanical stiffness and bony content in the poorly controlled DM rats. To determine the effect of BG control, DM rats were treated with insulin sufficient to maintain physiologic BG levels throughout the course of the study. Values of cellular proliferation, biomechanical properties and callus bone content in tightly controlled DM animals were not significantly different from values of non-DM control values. This study suggests that insulin treatment with resultant improved BG control will ameliorate the impaired early and late parameters of DM fracture healing.