Cerebral oedema (CO) is a rare life-threatening complication of diabetic ketoacidosis (DKA) in children. We analysed the biochemical and therapeutic risk factors for CO in DKA by a retrospective review of 256 children hospitalized for DKA between February 2003 and March 2015. The demographic characteristics, biochemical variables and therapeutic interventions were compared between the patients with and without CO. CO was observed in 22 (8.6%) of the 256 subjects included in the study. One of these patients (5%) had a fatal outcome and two patients (9%) survived with neurological consequences. CO was significantly associated with severe DKA: lower initial venous pH (p < 0.001) and bicarbonate (p < 0.001), higher initial blood glucose (p < 0.01), urea level (p < 0.05) and baseline serum osmolality (p < 0.05). During the treatment of DKA, low serum phosphate level was found to be significantly associated with CO (p < 0.05). We also found significant dependence between the development of CO and the initiation of treatment for DKA in another facility before hospitalization in our hospital (p < 0.05), bicarbonate application (p < 0.001), higher fluid volume infused initially (p < 0.01) and delayed potassium substitution (p < 0.01). Severe ketoacidosis, hyperglycaemia and dehydration at presentation, and low serum phosphate during treatment are significantly related to CO formation in children with DKA. The initial severe acidosis and hyperglycaemia probably cause brain injury which progresses into CO in the course of developing hypophosphatemia and cerebral hypervolemia.