Recent progress in non invasive diagnostic techniques for the study of the microcirculation, evoked a great interest in the screening of the patients with a diabetic microangiopathy. The authors, in this paper, wanted to evaluate the usefulness of photoplethysmography in the study of the microcirculation in children affected by type I diabetes; this technique was proposed as very reliable, non invasive and easily repeatable. 42 diabetic patients, with an age from 6 to 18 years, and a group of 12 healthy subjects of the same age, as a control group, were considered. Two particular points of interest were found: the statistical correlation between familial pathology for a vascular disease and the photoplethysmographic findings and the significant correlation between the age of the pathology and the beginning of the microcirculation disease. The authors, from their experience, evaluate the photoplethysmography as a reliable technique in the screening of all the diabetic subjects, children and adults, to evidence, as soon as possible, eventual lesions of the microcirculation for the beginning of an adequate therapy.