The arterioles in the cremaster muscle of 8 to 10-week-old Ob/Ob, Db/Db and stroptozotocin diabetic mice are characterized by a decreased number of arterioles, loss of vascular tone and a reduced cross-sectional area of the vessel walls. The present study was designed to determine if these abnormalities persist to adult life or if additional abnormalities develop to cause vascular dysfunction. The diameters, wall thickness to lumen ratios and vessel wall areas of comparable types of innervated arterioles in 24- to 28-week-old normal and Db/Db mice are equivalent, except that the smallest arterioles of Db/Db have thin vessel walls. However, blood flow at rest is only 3.0 ± 0.9 ml/min/100 g of cremasteric muscle tissue in Db/Db mice as compared to 5.5 ± 1.3 ml/min/100 g in normal mice. After all vascular control is abolished, the arterioles of Db/Db dilated, but significantly (p < 0.05) less than in normal animals. The minimum distance between adjacent capillaries (wall to wall) during the passive state was 28 ± 1.7 µm in Db/Db mice and 21.8 ± 0.6 µm in normal mice; this indicates a major decrease of vascularity in the adult Db/Db mouse. The results obtained indicate that the reduction in numbers of arterioles and loss of vascular tone in juvenile diabetic mice persists to adult life but arteriolar wall characteristics become normal in adult