Multiple symmetric lipomatosis (MSL) is a rare disorder characterised by large subcutaneous fat masses in some parts of the trunk, Mitochondrial disfunction is common in MSL, but the identity of the adipose cells developing in multiple lipomas is not well known. We determined that brown adipose tissue-specific uncoupling protein-1 (UCP-1) mRNA is expressed in the lipoma of a multiple symmetric lipomatosis patient bearing the 8344 mutation in the tRNALys gene of mitochondrial DNA. UCP1 mRNA was not detected in normal subcutaneous fat from the same patient or in the lipoma of another patient bearing a different mutation in the same tRNALys gene. These findings implicate brown adipose cells as the origin of lipomas in a subset of patients bearing tRNALys mutations in mitochondrial DNA.