Maturity-onset diabetes of the young (MODY) is a rare form of juvenile diabetes mellitus that presents with hyperglycaemia in the absence of ketosis. We present three cases of MODY, all of whom had pedigrees with diabetics in multiple generations. All our patients presented in adolescence with evidence of insulin resistance. Two patients were relatively overweight. All three patients were readily controlled on diet alone. None had any clinical evidence of diabetic complications in early adulthood. Recently there has been a marked increase in our understanding of MODY. Genetic linkage and mutational analyses have identified three subtypes (MODY1, 2 and 3) that are all transmitted in an autosomal dominant fashion. The pathophysiology of the MODY subtypes is variable with both increased and decreased insulin levels being seen. A failure to recognise MODY will result in a lack of appropriate therapy and the potential for diabetic complications.