Objective: Dentists in the National Dental Practice-Based Research Network (NationalDentalPBRN.org) are offered online and mailed options for some network questionnaires. We quantified differences in (1) characteristics of dentists who completed a questionnaire online compared to using a mailed option, and (2) prevalence estimates for select practice characteristics [e.g., use of an electronic dental record (EDR), rubber dam during root canal treatment, and expanded-function auxiliaries (EFA)] between online and mailed completers. Method: Invitation letters were sent by the network’s central administrative site to eligible practitioners providing them a unique identification number and log-in code to complete the online survey. Eligibility consisted of prior participation in any network study and currently practicing dentistry. Practitioners were asked to complete the questionnaire within three weeks; non-respondents received a reminder letter after the fourth week. After an additional four week period, a final reminder was sent, along with a printed questionnaire version allowing the option of completing via online or paper. Of 632 US dentists completing the survey, 84 (13%) used the mailed version. Result: Completion by mail (paper) was more common among males, older dentists and those in general practice (p< 0.05). Response mode did NOT differ significantly by either practice setting (solo, large group practice, or public health) or region of the country, in either bivariate or adjusted analyses. Paper completion was less common among practices with EDR (11% vs. 20%, p=0.01), those consistently using rubber dam (8% vs. 16%, p=0.007), and those who have ever worked with or employed EFA (9% vs. 17%, p=0.008). The differences with EDR and consistent use of rubber dam remained significant in adjusted models. Conclusion: Not including an option to allow completion by paper would have resulted in overestimation of key practice characteristics among network dentists.