This study explored the effects of problem-oriented dental ethics curriculum, consisting of 39 contact hours distributed over four years on moral reasoning development and on attitudes about the value of instruction. Students (n = 720) in the classes of 1985 through 1992 participated in the required curriculum and completed, as freshman and seniors, the Defining Issues Test (DIT), a well-validated test of moral reasoning. In addition, students responded to open-ended questions about the value of ethics instruction. Cross-sectional comparison of the eight classes of entering freshman with two classes of third quarter juniors (n = 265) who completed the DIT prior to implementing the ethic curriculum indicated that the dental curriculum offered prior to 1981 had little influence on moral reasoning. Pre- to posttest DIT comparisons for seven of the eight classes of instructed students indicated statistically significant improvement. Comparison of the effect sizes (Cohen's d) of our intervention with the average effect size reported in a meta analysis of effective interventions indicates that results cannot be attributed to student maturation alone. Analysis of individual change patterns suggest that the success occurred despite a higher than average (17 percent vs. 6 percent) number of students who showed regression from pre- to posttest. Substantive explanations (gender, motivation, regression to the mean) did not appear to account for the change patterns, but theoretical explanations, based on observations in other settings, offer insights for further research and curriculum development. In conclusion, the results indicate that students not only benefit from ethics instruction, but value it.