Hepatocerebral mitochondrial DNA depletion syndromes are classically considered diseases of early childhood, typically affecting the liver, peripheral, and central nervous systems with a rapidly progressive course. Evidence is emerging that initial symptom onset can extend into adulthood, though few such cases have been reported. We describe a 25-year-old woman who presented initially with secondary amenorrhea, followed by a megaloblastic anemia, lactic acidosis, leukoencephalopathy, progressive peripheral neuropathy, and liver cirrhosis. An apparently homozygous P98L mutation was identified in MPV17, a gene associated with a lethal infantile neurohepatopathy. Homozygosity for the same allele was recently reported in a man with a similar hepatic and neurologic phenotype. This is the first clinical report of an adult female with this disorder, and the first to describe amenorrhea and megaloblastic anemia as likely associated symptoms.