© 2014 American Association of Public Health Dentistry. Objective Dentists in the National Dental Practice-Based Research Network are offered online and mail options for most questionnaire studies. We sought to quantify differences a) in characteristics of dentists who completed a questionnaire online as compared with those who completed a mail option offered to online nonresponders and b) in prevalence estimates for certain practice characteristics. Methods Invitation letters to participants provided an identification number and log-in code with which to complete the online survey. Nonrespondents received a reminder letter after the fourth week, and after an additional 4-week period, a final reminder was sent, along with a paper questionnaire version, allowing completion online or by paper. Results Of 632 US dentists who completed the survey, 84 (13 percent) used the paper version. Completion by paper was more common among males, older dentists, and those in general practice (P-<-0.05). The proportions of dentists who used electronic dental records, who consistently used a rubber dam when performing root canals, and who either worked with or employed expanded-function auxiliaries were lower among dentists who completed the survey using the paper-mail version than among those who completed it online; these differences remained significant in models adjusted for gender, age, and practice type. Conclusion Even in an era of increasingly electronic communication by dentists, not including a paper option when conducting surveys can result in overestimation of the prevalence of key dental practice characteristics.