Aims To assess the effects of a workshop on supportive leadership behaviour (SLB) on the performance of head nurses, using a randomized controlled trial design. Background The effect of transformational leadership on SLB in nursing management is emphasised. Methods A total of 110 head nurses working at university hospitals were included randomly in two control and intervention groups. The head nurses in the intervention group participated in supportive leadership training, but the control group did not. Performance in supportive leadership was assessed with a validated instrument, which six subordinates used to assess their head nurse (n=731). Results There was a significant difference in SLB scores from baseline to the 3month follow-up (P<0.0001). Moreover, the post-intervention scores were significantly higher in the intervention group, compared with the control group (P<0.0001). The results showed that in the intervention group, the effect sizes were greater for males (50%) than for females (36%) and greater for married participants (42%) than for single participants (37%). Conclusion The workshop on supportive leadership behaviour, particularly the interactive multifaceted training, improved the leadership performance of the head nurses who participated in this study. Implications for nursing managers Health policy decision makers should apply SLB, which is a significant leadership style, to improve the outcomes in other groups of health-care management, such as physicians. Future studies are needed to investigate the effects of such workshops in longer periods of follow up.