Abstract Background Early clinical exposure (ECE) is viewed as a way to provide contexts of basic science and highlight its relevance to medical practice. However, very few studies have specifically looked into how the ECE experience contributes to students’ academic performance. The purpose of this study was to investigate whether ECE experiences (external cause) or students’ learning attitudes (internal cause) more closely correlated with medical students’ academic performance. Methods Subjects who participated in the study comprised 109 s-year students at Taipei Medical University. Fifty of the 109 study participants were enrolled in an elective ECE program. The dependent variable in this study was the test score of a systems-based basic sciences (SBBS) course. Independent variables of the study included students’ attitudes and test anxiety towards the SBBS course, engagement/length of time spent in ECE, and the ECE learning environment. Data of students’ engagement in ECE, levels of their motivational beliefs and test anxiety, differences in the ECE learning environment, and the SBBS final test scores of these 109 respondents were collected for hierarchical multiple regression (HMR) analyses. Results Results of the HMR analyses revealed that students’ test anxiety towards basic science and also the learning environment of the ECE had significant positive predictive power on their SBBS test scores. Conculsion This study discovers that medical students’ academic performance in basic science correlates not only with their anxiety to testing, but even more so with the clinical environment they are exposed to. Hence we suggest including further investigations about different learning environments on ECE experiences in future studies.