Objective: This practice-based study involved private practitioners who reported on the location of 1,100 sites of clinically diagnosed secondary caries. Method and materials: The secondary caries was noted on schematic diagrams on which the clinicians made an outline of the restoration and marked the location of the caries with a red pen. The secondary caries was classified as being located gingivally, occlusal/incisally, or at any other location of the restoration. Results: Overall, 80% to 90% of the clinically diagnosed secondary caries was reported to be located gingivally, irrespective of the type of restoration or restorative material employed. Class II restorations, analyzed separately, showed a slightly higher relative proportion of occlusal secondary caries on resin composite (16%) than on amalgam (8%) restorations. Conclusion: A number of patient, operator, and material factors may contribute to the development of secondary caries and in the differential diagnosis of marginal discrepancies, including secondary caries, at the gingival area of restorations.