The aim of this study was to evaluate the past 10-year status of insulin therapy for preschool-age children with type 1 diabetes in Japan. One-hundred and forty-two patients who had been diagnosed at less than 5 years of age within the past 10 years (1993-2002) at 36 hospitals were registered in this study on April 2003. The methods of daily insulin therapy and episodes of severe hypoglycemia during the preschool period were investigated. Eighty-six (60.6%) children were treated with a pen-type device and 56 (39.4%) were treated with a syringe-type device. The once-a-day insulin regimen was used for 2, a twice-a-day regimen for 104, a three-times-a-day for 28 and a four-times-a-day for 8. Episodes of severe hypoglycemia were recorded in nearly half of the subjects, and one-fourth of the subjects had repeated episodes. One hundred and eleven of their parents were questioned regarding the degree of psychosocial stress experienced during the care of their children. Most parents worried about the glycosylated hemoglobin value at each hospital visit. They were next very afraid of nocturnal severe hypoglycemia, independent of any actual experience. These results suggest that although insulin therapy can involve various methods, the important point is to simultaneously provide good glycemic control and prevent severe hypoglycemia, especially during this age.