Background: The Dental Practice-Based Research Network (DPBRN) provided a means to investigate whether certain procedures were performed routinely. The authors conducted a study to quantify rubber dam use during root canal treatment (RCT) among general dentists and to test the hypothesis that certain dentist or practice characteristics were associated with rubber dam use. Methods: DPBRN practitioner-investigators (P-Is) answered a questionnaire that included items about rubber dam use and other forms of isolation during RCT. DPBRN enrollment questionnaire data provided information regarding practitioner and practice characteristics. Results: Atotal of 729 (74 percent) of 991 P-Is responded;524 were general dentists who reported providing at least some RCTs and reported the percentage of RCTs for which they used a rubber dam. Of these 524 P-Is, 44 percent used a rubber dam for all RCTs, 24 percent used it for 51 to 99 percent of RCTs, 17 percent used it for 1 to 50 percent of RCTs, and 15 percent never used it during RCT. Usage varied significantly by geographic region and practice type. The use of cotton rolls and other forms of isolation also was reported. Conclusions: Similar to other reports in the literature, not all DPBRN general dentists used a rubber dam during RCT. Clinical Implications: Because the clinical reference standard is to use a rubber dam during RCT, increasing its use may be important.