Aspiring to become a physician is a natural expectation for applicants to medical school. However, choosing a career in medicine is a critical decision, especially in countries where high school students can apply to medical school without an undergraduate degree. Students may select a medical career for various reasons, including parental pressure and academic performance. The question of whether there are students who enroll in medical school without clear intentions of becoming doctors has not been extensively investigated in the literature. We conducted a retrospective study at a national university in Japan. Given the scarcity of research examining medical students who did not have a clear intention to become doctors at the time of admission, we created a survey. The questionnaire asked students whether they had clear intentions to become doctors upon enrollment, and those who responded affirmatively were defined as students with clear intentions to become doctors at admission and assigned to the first group. The second group was composed of students who entered medical school without clear intentions to become doctors. We then compared the differences in sociodemographic characteristics and career determinants between these groups using statistical methods, including Chi-square tests and logistic regression. The collection rate of the questionnaire was 76.2%. We found that 28.8% of students at a national medical school in Japan entered medical school without clear intentions of becoming doctors. For these students, 'parental expectations' and 'peer influence' were identified as significant career determinants. No sociodemographic characteristics showed significant associations with the ambiguity of students' intentions to pursue a medical career at admission. This study confirmed that some students enroll in medical school without clear intentions of becoming doctors. The background factors related to this type of student were parental expectations and the influence of peers on career choice.