Background: The randomized case presentation (RCP) study was designed to assess the degree of diagnostic accuracy for described periodontal cases. This was to lay the basis for practitioner calibration in the Network for future clinical studies. Methods: The RCP consisted of ten case scenarios ranging from periodontal health, gingivitis, mild, moderate, and severe periodontitis. Respondents were asked for their diagnosis of the described cases. Survey diagnoses were compared to two existing classifications of periodontal disease status. The RCP was administered via a proprietary electronic data capture system (Advantage EDC(®)) maintained by the Practitioners Engaged in Applied Research and Learning's (PEARL's) Data Coordinating Center(‡). Standard analytic techniques including frequency counts and cross-tabulations were used for categorical data with mean and standard deviation and median values reported for continuous data elements. Results: Demonstrable variations in periodontal assessment for health, gingivitis, mild, and moderate, and severe periodontitis were found among 130 PEARL general practitioners who participated in the RCP survey. The highest agreement for diagnosis among dentists was found (88%) for severe periodontitis. The range of agreement among dentists for all ten case presentations was 55% to 88% representing the cases described from health to severe periodontitis. The highest percentage of the variation was found in cases with health and gingivitis. Conclusion: There was variation among PEARL practitioners in periodontal diagnosis which may affect treatment outcomes. Our findings add clinical support to recent publications suggesting a need for standardization of terminology in periodontitis diagnosis.