Maternally inherited deafness and diabetes (MIDD) is characterised by a defect in insulin secretion and bilateral hearing impairment. The m.3243A>G mutation is the most reported in mitochondrial DNA (mtDNA) causing MIDD, although other, rare, mtDNA point mutations have also been mentioned. We report on a 28-year-old Caucasian woman with a history of diabetes, kidney disease, deafness, diarrhoea, myopathy and fatigue. The diagnosis of mitochondrial disease was made in this patient, which resulted from a novel 09155A>G mutation in the mtDNA. As far as we know, this mutation has never been described before as causing MIDD.