Case report on a child whose type I diabetes mellitus was diagnosed 23 months before the appearance of overt glucose intolerance. In this pre-IDDM stage of DMI were observed secondary enuresis, decreased growth speed, transient hyperglycemia and asymptomatic glycosuria. These alterations may represent the earliest clinical manifestation of impaired beta cell function. Immunologic markers (ICA and/or AAI) of DMI and abnormalities of the first-phase insulin secretion in response to intravenous glucose also may precede by several months the most common clinical picture of type I diabetes as they were detected in this child. If possible, markers and alterations should be tested in such patients and their young relatives with DMI in order to detect high risk individuals who may develop DMI. Such and accurate predictive ability should be a prerequisite to institution of appropriate therapy to preventing further beta cell destruction and severe metabolic decompensation, thus having the potential to reduce morbidity and mortality from new onset DMI.