Objective: To describe the diagnostic techniques used by Dental Practice-Based Research Network (DPBRN; www.DPBRN.org) dentists to detect primary caries lesions, on occlusal, smooth and proximal surfaces of anterior and posterior teeth. Methods: A total of 229 DPBRN dentists recorded information on 8,351 restorations inserted due to primary caries lesions on 5,810 patients. DPBRN comprises five regions: Alabama/Mississippi, Florida/Georgia, Minnesota, Permanente Dental Associates, and Scandinavia. Statistical analysis utilized generalized mixed-model ANOVA, in order to account for the hierarchical structure of the data. Practitioner-investigators placed a mean (S.D.) of 43.2 (14.8) restorations for this study. A total of 95% of eligible consecutive patients enrolled in the study. For this analysis lesions were categorized as: posterior proximal, anterior proximal, posterior occlusal, posterior smooth and anterior smooth. The data collection form asked what technique was used to diagnose the primary caries lesion. The options included clinical assessment, radiographs, and optical techniques. Results: Diagnostic technique was significantly associated with lesion category after adjusting for clustering in dentists (p< 0.0001). We did not identify an association of diagnostic technique by DPBRN region (p=.2910). Diagnostic techniques used most frequently for each lesion category: clinical assessment plus radiographs for posterior proximal (47%), clinical assessment for anterior proximal (52%), clinical assessment for posterior occlusal (46%), clinical assessment for posterior smooth (77%) and clinical assessment for anterior smooth (79%). Conclusion: These results, obtained from clinical procedure reporting rather than questionnaires, document diagnostic techniques used by practicing dentists in actual delivery of restorative care. Diagnostic technique varied by lesion category. Support: U01-DE-16746, U01-DE-16747.