Converging evidence implicates mitochondrial dysfunction in bipolar disorder (BPD). Treatments of adolescent BPD have limited efficacy, and are associated with significant toxicity. Phosphorus magnetic spectroscopy imaging (31P MRSI) may shed light on the pathophysiology and neural markers of adolescent BPD. In the present study, nicotinamide adenine dinucleotide (NAD) levels were measured using 31P MRSI in 15 adolescents with BPD and 23 healthy controls (HC). BPD adolescents had significantly decreased NAD levels compared to HC. Clinical trials of NAD precursors are required to determine whether restoration of NAD levels is feasible, and can serve as a treatment for adolescent BPD.