Routinely collected Scottish hospital discharge data were used to identify newly diagnosed cases of diabetes mellitus under the age of 19 years. In the period 1977-83 there were 2183 cases, an average annual incidence of 21.0 per 100,000 per annum. This rate is one of the highest reported and represents a continuation of the increase in incidence which occurred during the period 1968-76. Statistically significant geographical variation in incidence was observed with the higher incidence in the least densely populated areas. Seasonal variation in the month of first admission was evident in all except the under-five age group with peaks occurring in winter. An estimated 60% of newly diagnosed cases were readmitted within 5 years and the pattern of readmission was found to differ little between males and females or between age groups.