Abstract Background The outcome of communication training is widely measured by self-efficacy ratings, and different questionnaires have been used. Nevertheless, none of these questionnaires have been formally validated through systematic measurement of assessment properties. Consequently, we decided to further develop a self-efficacy questionnaire which has been used in previous studies. This study aims to examine the content, internal structure, and relations with other variables of the new version of the self-efficacy questionnaire (SE-12). Methods The questionnaire was developed on the basis of the theoretical approach applied in the communication course, statements from former course participants, teachers, and experts in the field. The questionnaire was initially validated through face-to-face interviews with 9 staff members following a test-retest including 195 participants. Results After minor adjustments, the SE-12 questionnaire demonstrated evidence of content validity. An explorative factor analysis indicated unidimensionality with highly correlated items. A Cronbachâ s Îą of 0.95 and a Loevingerâ s H coefficient of 0.71 provided evidence of statistical reliability and scalability. The test-retest reliability had a value of 0.71 when evaluated using intra-class correlation. Expected relations with other variables were partially confirmed in two of three hypotheses, but a ceiling effect was present in 9 of 12 items. Conclusions The SE-12 scale should be regarded a reliable and partially valid instrument. We consider the questionnaire useful for self-evaluation of clinical communication skills; the SE-12 is user-friendly and can be administered as an electronic questionnaire. However, future research should explore potential needs for adjustments to reduce the identified ceiling effect.