Type 1 diabetes mellitus (DM1) is linked to a decrease in bone strength. Bone strength entails both bone mineral density and bone quality. Limited data are available regarding diabetes-induced microdamage, which can severely infuence bone quality. This study has investigated bone microdamage as a measure of bone quality in an animal model of DM1. Microdamage in the neck of the femur was labelled in vivo using multiple fuorochromes at 4, 12 and 24 weeks after the onset of DM1. Microcracks were quantifed and their morphology analyzed using microscopy techniques. The mean length of microcracks at 24 weeks, and crack numerical and surface densities were signifcantly higher (p<0.05) 4 weeks after the onset of DM1 when compared with control. Difuse damage density was highest at 12 weeks after the onset of DM1. The arrangement of the collagen fbrils became progressively more irregular from 4 to 24 weeks of DM. This is the frst study to analyze microdamage in vivo at diferent time points of DM1. DM1is associated with microcracks from the early stage, however bone microstructure shows toughening mechanisms that arrest their growth but disease progression further deteriorates bone quality resulting in longer microcracks which may increase fracture risk.