Background: For the purpose of providing excellent patient care, residents need to be strong, effective leaders. The lack of clinical leadership is alarming given the detrimental effects on patient safety. The objective of the study was to assess whether a leadership training addressing transactional and transformational leadership enhances leadership skills in residents. Methods: A volunteer sample of 57 residents from postgraduate year one to four was recruited across a range of medical specialties. The residents took part in an interventional controlled trial. The four-week IMPACT leadership training provided specific strategies for leadership in the clinical environment, addressing transactional (e.g. active control, contingent reward) and transformational leadership skills (e.g. appreciation, inspirational motivation). Transactional and transformational leadership skill performance was rated (1) on the Performance Scale by an external evaluator blinded to the study design and (2) self-assessed transformational and transactional leadership skills. Both measures contained items of the Multifactor Leadership Questionnaire, with higher scores indicating greater leadership skills. Results: Both scores were significantly different between the IMPACT group and the control group. In the IMPACT group, the Performance Scale increased 15% in transactional leadership skill performance (2.10 to 2.86) (intervention effect, 0.76;95% CI, 0.40 to 1.13;p < .001, eta(2) = 0.31) and 14% in transformational leadership skill performance (2.26 to 2.94) (intervention effect, 0.68;95% CI, 0.27 to 1.09;p < .001, eta(2) = 0.22). The self-assessed transactional skills revealed a 4% increase (3.83 to 4.03) (intervention effect, 0.20;95% CI, 0.08 to 0.33;p < .001, eta 2 = 0.18) and a 6% increase in transformational leadership skills (3.54 to 3.86) (intervention effect, 0.31;95% CI, 0.02 to 0.40;p < .001, eta(2) = 0.53). Discussion and conclusions: These findings support the use of the transactional and transformational leadership framework for graduate leadership training. Future studies should incorporate time-latent posttests, evaluating the stability of the behavioral performance increase.