BackgroundGeneral practitioners (GPs) experience barriers to the use of evidence-based medicine (EBM) related to a negative attitude and to insufficient knowledge and skills. We therefore designed a blended learning intervention to develop the competence of GP trainers in EBM. This study investigated the effectiveness of this intervention in increasing the trainers’ EBM competencies (i.e. knowledge, skills, attitude and behaviour).MethodsIn total 129 GP trainers participated in the blended learning course on EBM consisting of four 3-h face-to-face meetings and an intensive preparatory e-course before each meeting over a 12-month period. The primary outcomes were changes in knowledge and skills (Fresno test), changes in attitude (McColl test) and intentions to change behaviour. Secondary outcomes were changes in self-rated knowledge, skills and attitude, and the relation between personal characteristics and changes in knowledge, skills and attitude. Data were collected before the start of the intervention (T0), at the end of the last day of the intervention (T1) and four months after the end of the intervention (T2).ResultsThe mean changes in scores on the Fresno test were ∆T1-T0 = 40.8 (SD ±36.7, p < .001) and ∆T2-T0 = 20.8 (±39.9, p < .001). The mean changes in scores on the McColl test were ∆T1-T0 = 2.2 (SD ±12.8, p = .16) and ∆T2-T0 = -.87 (±10.0, p = .49). Of the GP trainers, 16.7 % fulfilled their intentions to change in behaviour, 47.6 % partly fulfilled them and 35.7 % did not fulfil them at all. Female trainers scored significantly higher on the Fresno test after the intervention compared to male trainers. There was a weak positive correlation between self-rated knowledge and the scores on the Fresno test. A moderate correlation was found between the overall score on the McColl test and self-rated attitude.ConclusionAn intensive blended learning course on EBM for GP trainers induces an increase in knowledge and skills that, although decreased, remains after four months. Attitude and behaviour towards EBM show no differences before and after the intervention, although GPs’ intention to use EBM more often in their practice is present.