A previously well 5-year-old girl presented with new onset type 1 diabetes mellitus and diabetic ketoacidosis, and was found to be profoundly hyperlipidaemic. Further investigations showed that she had associated hypothyroidism. She responded to insulin and L-thyroxine treatments and her lipid profile returned to normal 2 months after diagnosis. Despite starting anticoagulant therapy early, she developed deep vein thrombosis of the lower limb. Her family screen did not demonstrate familial hyperlipidaemia or hypothyroidism. We discuss our patient's diagnosis and management and highlight the challenges faced in this case. A lipid profile may be warranted in cases of concomitant diabetes and hypothyroidism to detect this problem and institute early treatment(s); monitoring for potential complications is warranted.