Medicine endorses a code of ethics and encourages a high moral character among doctors. This study examines the influence of medical education on the moral reasoning and development of medical students. Kohlberg's Moral Judgment Interview was given to a sample of 20 medical students (41.7% of students in that class). The students were tested at the beginning and at the end of their medical course to determine whether their moral reasoning scores had increased to the same extent as other people who extend their formal education. It was found that normally expected increases in moral reasoning scores did not occur over the 4 years of medical education for these students, suggesting that their educational experience somehow inhibited their moral reasoning ability rather than facilitating it. With a range of moral reasoning scores between 315 and 482, the finding of a mean increase from first year to fourth year of 18.5 points was not statistically significant at the P < or = 0.05 level. Statistical analysis revealed no significant correlations at the P < or = 0.05 level between the moral reasoning scores and age, gender, Medical College Admission Test scores, or grade point average scores. Along with a brief description of Kohlberg's cognitive moral development theory, some interpretations and explanations are given for the findings of the study.