BACKGROUND: Motor dysfunction is a primary feature of Parkinson’s disease (PD), with postural instability, one of the key features that lead to an increased likelihood of falls. This study investigated whether Transcranial Direct Current Stimulation tDCS has a beneficial effect on balance control during single task and dual task conditions while standing on stable and unstable surfaces in people with Parkinson’s’ disease. METHODS: tDCS (1 mA; 20 minutes) was applied with the anode electrode (5x7 cm2) over the Left-DLPFC, and the cathodal electrode (10x10 cm2) over the right supraorbital area. 16participants with early stage PD (65.38 ± 9.722 years) completed four single tDCS sessions in a randomised order: real or sham stimulation, whilst standing on stable or unstable surface. There were four testing blocks (1 pre-stimulation, 2 start of stimulation, 3 middle of stimulation, 4 post-stimulation). In each block there were three single task and three dual-task trials (30 s). Path length (PL) from force plate centre of pressure (COP) was recorded and analysed; increased PL indicates greater postural instability. RESULTS: Path length COP was greater during stimulation compared to sham (p<001), on the unstable compared to the stable surface, (p<0.001), and during the dual task compared to the single task,(p<0.001). There was a significant block effect: PL was decreased during the Post-stimulation block relative to the Pre-stimulation block (P=0.042). There was a Surface x Block interaction (p=0.024). On the stable surface PL was decreased on Block 2 relative to Block 1 (p=0.048). On the unstable surface Block 4 (post stimulation) PL was decreased relative to all other blocks. CONCLUSIONS: In contrast to expectation, real tDCS increased postural instability. tDCS had no effect relative to the cognitive task (single task vs dual task) or surface (firm vs foam). REAL WORLD IMPLICATIONS: Prior to a possible clinical application, tDCS parameters that lead to beneficial stimulation effects have to be identified.