Diabetic ketoacidosis is the most serious acute complication of insulin-dependent diabetes mellitus and the most frequent reason for hospital admission of diabetic children. The most frequent cause of death of these patients is also the diabetic ketoacidosis. The mortality rate of the disease has not changed since the seventies (1-2%). In this work, the data of 89 patients with diabetic ketoacidosis were analyzed. These patients were admitted to the 1. Department of Pediatrics of the Semmelweis University of Medicine between 1992-1997. The data (metabolic parameters, the causes of ketoacidosis and the length of hospital stay) of previously known diabetic children was compared with the data of previously unknown diabetic children. Our patients were divided in 2 groups: serious (n = 11), and mild-to-moderate (n = 48) acidosis. Their laboratory findings, their intravenous infusion-, and insulin demand and the length of their hospital stay were compared. The state of consciousness at their hospitalisation and the concomitant complications were also examined. Significant difference was found only in the duration of intravenous insulin administration (with the exception of pH and BE, of course). There was no relationship between the seriousness of the disease and the duration of hospital treatment. It is noteworthy that even the previously known diabetic children with the shortest hospitalization spent more than 7 days at the department.