To identify underlying causes for failure of medical thesis projects and the constantly high drop-out rate in Germany from the supervisors' perspective and to compare the results with the students' perspective.Cross-sectional survey. Online questionnaire for survey of medical thesis supervisors among the staff of Charité-Universitätsmedizin Berlin, Germany. Published, earlier longitudinal survey among students for comparison.1069 thesis supervisors participated.Data are presented using descriptive statistics, and the χ test served to compare the results among supervisors with the earlier data from the longitudinal survey of doctoral students.Not applicable. This survey is an observational study.Of 3653 potential participants, 1069 (29.3%) supervising 3744 doctoral candidates participated in the study. Supervisors considered themselves to be highly motivated and to offer adequate supervision. On the other hand, 87% stated that they did not feel well prepared for thesis supervision. Supervisors gave lack of timeliness of doctoral students and personal differences (p=0.024 and p=0.001) as the main reasons for terminating thesis projects. Doctoral students predominantly mentioned methodological problems and difficult subjects as critical issues (p=0.001 and p<0.001). Specifically, students felt ill prepared for the statistical part of their research-49.5% stated that they never received statistical assistance, whereas 97% of supervisors claimed to help their students with statistical analysis.The authors found that both thesis supervisors and medical students feel ill prepared for their roles in the process of a medical dissertation. Contradictory reasons for terminating medical thesis projects based on supervisors' and students' self-assessment suggest a lack of communication and true scientific collaboration between supervisors and doctoral students as the major underlying issue that requires resolution.