Objectives: The aim of this study was to evaluate the validity of partial CPITN (PCPITN) and full-mouth CPITN (FCPITN) indexes from CPITN index versions used in the diagnosis of periodontal disease. Method: The study included 1,000 patients over the age of 20. The clinical attachment loss examination and clinically assisted full-mouth periodontal examination (gold standard) including the depth of the periodontal pocket on probing and dental stones were performed. PCPITN and FCPITN index versions were compared with the gold standard oral examination. Sensitivity, specificity and diagnostic estimation tables were statistically created from the obtained data. Results: For Gingivitis, the sensitivity of the PCPITN index was found to be 68.88%, specificity was 85.94% and the field value under the Receiver Operating Characteristic (ROC) curve was 0.6893. For periodontitis, FCPITN index sensitivity was 89.28%, specificity was 96.56% and field value under the ROC curve was 0.931. Conclusion: Although FCPITN and PCPITN indexes have a near moderate value in the diagnosis of gingivitis, they were found to be more effective in the diagnosis of periodontitis. We think that the FCPITN index is particularly effective in the diagnosis of periodontitis. How to cite this article: Tanık A, Gül M. The validity of the Community Periodontal Index of Treatment Needs (CPITN) in Epidemiological Studies of Periodontal Diseases. Int Dent Res 2020;10(2):44-48. https://doi.org/10.5577/intdentres.2020.vol10.no2.3 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.