Performance on long delays of delayed response tasks is associated with medial temporal function, a region of the brain affected by severe hypoglycemia. A previous study showed that children with type 1 diabetes mellitus (T1DM) with higher risk for severe hypoglycemia performed worse than controls on long delays of a spatial delayed response (SDR) task. We tested the more specific hypothesis that frequency of severe hypoglycemia would relate to long delay SDR performance. Children with T1DM (n = 51) and controls (n = 32) performed the SDR task with short and long delays. Information was collected on children's past severe hypoglycemia. In children with T1DM, number of past severe hypoglycemic episodes accounted for a significant portion of the variance in long delay SDR after controlling for age and age of onset. This relationship was not seen with short delay SDR or with other tasks (verbal or object memory, attention, motor speed). These results support the hypothesis that severe hypoglycemia has specific, negative effects on memory skills in children. If this relationship is extrapolated to children with higher frequency of severe hypoglycemia, due to longer duration of disease or poorer glucose control, it may affect daily functioning and thus need to be considered in treatment decisions. (JINS, 2003, 9, 740–750.)