The lipoprotein lipase coding gene sequence was analysed on a 10-year-old girl with new-onset Type 1 diabetes mellitus (DM), ketoacidosis and severe hypertriglyceridaemia (TG > 112.9 mmol/l), revealing that the patient was a compound heterozygote for two mutations, D9N in exon 2 and S447X in exon 9. Although these two mutations usually do not considerably impair lipolytic enzyme activity, the combination of both in this patient may play a role in the development of severe hypertriglyceridaemia.