This proof-of-concept, double-blind study was designed to determine the effects of transcranial direct current stimulation (tDCS) on the ‘cost’ of performing a secondary cognitive task on gait and postural control in healthy young adults. Twenty adults aged 22 ± 2 years completed two separate double-blind visits in which gait and postural control were assessed immediately before and after a 20 min session of either real or sham tDCS (1.5 mA) targeting the left dorsolateral prefrontal cortex. Gait speed and stride duration variability, along with standing postural sway speed and area, were recorded under normal conditions and while simultaneously performing a serial-subtraction cognitive task. The dual task cost was calculated as the percent change in each outcome from normal to dual task conditions. tDCS was well tolerated by all subjects. Stimulation did not alter gait or postural control under normal conditions. As compared with sham stimulation, real tDCS led to increased gait speed (P = 0.006), as well as decreased standing postural sway speed (P = 0.01) and area (P = 0.01), when performing the serial-subtraction task. Real tDCS also diminished (P < 0.01) the dual task cost on each of these outcomes. No effects of tDCS were observed for stride duration variability. A single session of tDCS targeting the left dorsolateral prefrontal cortex improved the ability to adapt gait and postural control to a concurrent cognitive task and reduced the cost normally associated with such dual tasking. These results highlight the involvement of cortical brain networks in gait and postural control, and implicate the modulation of prefrontal cortical excitability as a potential therapeutic intervention.