BACKGROUND Insulinomas are pancreatic neuroendocrine tumors that cause non-ketotic hypoglycemia due to hyperinsulinism; they are extremely rare, especially in children. CASE REPORT We present a case of a sporadic insulinoma in an 11-year-old boy who had episodes of self-limited drowsiness and behavior changes over a 3-month period, thought to be caused by psychological issues. Non-ketotic hypoglycemia was confirmed at our center. A fasting blood test found inappropriately elevated insulin levels during hypoglycemia, undetectable β-hydroxybutyrate, and increased C-peptide levels in line with insulin levels. Anti-insulin antibodies were negative and antidiabetic drugs untraceable. The glucagon-stimulation test was positive. Growth hormone, adrenocorticotropin hormone, and phosphorus and calcium metabolism were normal. Dual-phase computed tomography detected a lesion compatible with an insulinoma. Endoscopic ultrasound showed a homogenous lesion at the junction of the body and tail of the pancreas. Histologic analysis of a fine-needle aspiration biopsy was compatible with neuroendocrine neoplasia. Preoperatively, a fractional diet avoiding fast-absorbing carbohydrates maintained normal glucose blood levels. Enucleation was not possible, so the lesion was resected along with portions of the body and tail of the pancreas. The well-differentiated tumor measured 15 mm x 13 mm. Postoperative blood glucose levels were correct, allowing a normal diet. CONCLUSIONS In children with unspecific symptoms compatible with hypoglycemia, blood glucose must be evaluated to confirm low blood glucose levels. Determining blood ketone levels is important for the differential diagnosis. The diagnostic approach to pediatric insulinoma represents a challenge for multidisciplinary teamwork.