Purpose: This study investigated the reliability of partial-mouth periodontal examinations (PMPEs) for 1) identifying the presence of periodontitis, 2) staging periodontal disease, and 3) reflecting mean clinical parameters. Methods: All patients were diagnosed using 8 different exam types: (A) full-mouth periodontal examination (FMPE), (B) Community Periodontal Index of Treatment Needs (CPITN) codes, (C) panoramic radiographs only, (D) clinical parameters only, (E) 6 teeth, including the first molar (#11, #16, #26, #31, #36, #46), (F) CPITN index teeth (#11, #16, #17, #26, #27, #31, #36, #37, #46, #47), (G) Ramfjord teeth (#16, #21, #24, #36, #41, #44), and (H) 10 modified Ramfjord teeth, including all first premolars and first molars (#16, #14, #21, #24, #26, #36, #34, #41, #44, #46). Case definitions were established according to the criteria outlined in the 2018 American Academy of Periodontology/European Federation of Periodontology classification of periodontal diseases. The accuracy of diagnosis and diagnostic performance were assessed using the kappa coefficient and area under the curve (AUC)/receiver operating characteristic analyses, respectively. To compare the mean clinical parameters, intraclass correlation coefficients (ICCs) were calculated between 4 types of PMPEs (E, F, G, H) and FMPE. Results: In total, 218 subjects (130 female, 88 male) were included in this study. Exam type F achieved perfect agreement (kappa coefficient: 1.0) in identifying the presence of periodontitis, and it showed almost perfect agreement in staging periodontal disease (0.85≤ kappa ≤0.98) except for the healthy category, with AUCs ≥0.97. Exam type H demonstrated the highest correlations of all mean clinical parameters with FMPE (ICCs ≥0.96). Conclusions PMPEs using the CPITN index teeth can be an excellent alternative for diagnosing periodontitis and staging its severity.