A concern about students' conceptual difficulties in organic chemistry prompted this study. It was found that prior knowledge from general chemistry was critical in organic chemistry, but what were some of the concepts that comprised that prior knowledge? Therefore an analysis of four years of organic chemistry quiz data was undertaken. Multiple general chemistry concepts were revealed that are essential prior knowledge in organic chemistry. The general chemistry concepts that were found pose a challenge to organic chemistry instructors who have identified those same concepts as ones they review or consider important in organic chemistry. A review of the literature provides recommendations that address the general chemistry students' difficulties revealed in this study. Further research, however, is needed to follow through on those recommendations.