Objectives This study aimed to establish the longterm effects of a 3-day 'Training for Trainers' course (TTC) on doctors' knowledge, teaching behaviour and clinical learning climate. Methods The study was designed as an intervention study with pre-, post- and long-term measurements. The intervention group (I-group) included 118 doctors from the departments of internal medicine and orthopaedic surgery at one university hospital. The control group (C-group) consisted of 125 doctors from the corresponding departments at another university hospital. Gains in knowledge about teaching skills were assessed by a written test. Teaching behaviour and learning climate were evaluated by questionnaires. Results In the I-group, 98.4% of doctors, both specialists and trainees, participated in a TTC. Response rates on the written test varied from 90% at baseline to 70% at 6 months after the intervention. Knowledge about teaching skills increased in the I-group by 25% after the TTC and was sustained at 6 months. Questionnaire response rates varied from 98.4% at baseline to 84.8% at 6 months. Post-course, the teaching behaviour of the I-group significantly changed and its learning climate improved compared with the C-group. Scores for use of feedback and supervision in the I-group increased from 4-5 to 6-7 (maximum score = 9). This was significantly higher than in the C-group. Conclusions A 3-day residential TTC has a significant impact in terms of gains of knowledge concerning teaching skills, teaching behaviour and learning climate after 6 months. The positive effects demonstrated in this study were rooted in both the specialists and trainees who attended the course.