Glucose metabolism in pancreatic β-cells elevates cytoplasmic [ATP]/[ADP], causing closure of ATP-sensitive K⁺ channels (K_ATP channels), Ca²⁺ entry through voltage-dependent Ca²⁺ channels, and insulin release. Decreased responsiveness of K_ATP channels to the [ATP]/[ADP] ratio should lead to decreased insulin secretion and diabetes. We generated mice expressing K_ATP channels with reduced ATP sensitivity in their β-cells. Previously, we described a severe diabetes, with nearly complete neonatal lethality, in four lines (A–C and E) of these mice. We have now analyzed an additional three lines (D, F, and G) in which the transgene is expressed at relatively low levels. These animals survive past weaning but are glucose intolerant and can develop severe diabetes. Despite normal islet morphology and insulin content, islets from glucose-intolerant animals exhibit reduced glucose-stimulated insulin secretion. The data demonstrate that a range of phenotypes can be expected for a reduction in ATP sensitivity of β-cell K_ATP channels and provide models for the corollary neonatal diabetes in humans.