Transcranial direct current stimulation (tDCS) has been proposed as a tool to enhance stroke rehabilitation; however, evidence to support its use is lacking. The aim of this study was to investigate the effects of anodal and cathodal tDCS on upper limb function in chronic stroke patients. Twenty five participants were allocated to receive 20 min of 1 mA of anodal, cathodal or sham cortical stimulation in a random, counterbalanced order. Patients and assessors were blinded to the intervention at each time point. The primary outcome was upper limb performance as measured by the Jebsen Taylor Test of Hand Function (total score, fine motor subtest score and gross motor subtest score) as well as grip strength. Each outcome was assessed at baseline and at the conclusion of each intervention in both upper limbs. Neither anodal nor cathodal stimulation resulted in statistically significantly improved upper limb performance on any of the measured tasks compared with sham stimulation (P>0.05). When the data were analysed according to disability, participants with moderate/severe disability showed significantly improved gross motor function following cathodal stimulation compared with sham (P=0.014). However, this was accompanied by decreased key grip strength in the unaffected hand (P=0.003). We are unable to endorse the use of anodal and cathodal tDCS in the management of upper limb dysfunction in chronic stroke patients. Although there appears to be more potential for the use of cathodal stimulation in patients with severe disability, the effects were small and must be considered with caution as they were accompanied by unanticipated effects in the unaffected upper limb.