Malnitrition-modulated diabetes mellitus ((MMDM) was previously known as protein-deficient diabetes mellitus (PDDM). Its clinical picture is similar to that of type 1 diabetes, but it develops over a background of chronic malnutrition from childhood. In spite of severe hyperglycemia, ketonuria never occurs. MMDM patients are extremely lean and require high doses of insulin-over 2.0 U/kg/day for good glycemic control. Even when optimally controlled, these patients maintain their leanness. Infections of the skin and soft tissues and pulmonary tuberculosis are often seen, whereas micro- and macrovascular complications are rare, even after long-term follow-up. Ultrasonographic evaluation of the abdomen clearly differentiates MMDM from fibrocalculous pancreatic diabetes. Absence of ketonuria and ketosis despite very severe hyperglycemia in emaciated young subjects is the most significant marker of MMDM.