Abstract Background The accuracy of self-assessment has been questioned in studies comparing physicians’ self-assessments to observed assessments; however, none of these studies used self-efficacy as a method for self-assessment. The aim of the study was to investigate how medical students’ perceived self-efficacy of specific communication skills corresponds to the evaluation of simulated patients and observers. Methods All of the medical students who signed up for an Objective Structured Clinical Examination (OSCE) were included. As a part of the OSCE, the student performance in the “parent-physician interaction” was evaluated by a simulated patient and an observer at one of the stations. After the examination the students were asked to assess their self-efficacy according to the same specific communication skills. The Calgary Cambridge Observation Guide formed the basis for the outcome measures used in the questionnaires. A total of 12 items was rated on a Likert scale from 1–5 (strongly disagree to strongly agree). We used extended Rasch models for comparisons between the groups of responses of the questionnaires. Comparisons of groups were conducted on dichotomized responses. Results Eighty-four students participated in the examination, 87% (73/84) of whom responded to the questionnaire. The response rate for the simulated patients and the observers was 100%. Significantly more items were scored in the highest categories (4 and 5) by the observers and simulated patients compared to the students (observers versus students: -0.23; SE:0.112; p=0.002 and patients versus students:0.177; SE:0.109; p=0.037). When analysing the items individually, a statistically significant difference only existed for two items. Conclusion This study showed that students scored their communication skills lower compared to observers or simulated patients. The differences were driven by only 2 of 12 items. The results in this study indicate that self-efficacy based on the Calgary Cambridge Observation guide seems to be a reliable tool.