Background Diabetes mellitus is the most common metabolic disease globally, while glucose-6-phosphate dehydrogenase deficiency, an X-linked inherited disorder, is the most common erythrocyte enzyme defect. The association between the two in children has been infrequently reported. Case presentation We report the case of a 10-year-old boy of Iraqi descent who presented to our emergency department with new-onset type 1 diabetes mellitus without Diabetic Keto Acidosis. He was treated with subcutaneous insulin and discharged. Eleven days after hospitalization, he was found to be jaundiced during his home visit. Hence, he was referred to the pediatric unit, and his hemoglobin had declined from 130 g/L at the previous admission to 81 g/L. Blood tests revealed low haptoglobin, and his peripheral blood film showed anisocytosis, polychromasia, and occasional red cell fragments suggestive of acute hemolysis. His glucose-6-phosphate dehydrogenase activity was very low, and his subsequent genetic tests confirmed Mediterranean-type glucose-6-phosphate dehydrogenase deficiency. Conclusion Glucose-6-phosphate dehydrogenase deficiency in people with diabetes mellitus has been underreported in the literature so far, and screening of glucose-6-phosphate dehydrogenase deficiency should be considered on diagnosis of diabetes mellitus, especially in boys of African, Mediterranean, or Asian descent.