Aims of this study were to comprehensively describe the intraoral distribution of the spirochete morphogroup and of 7 antigenically distinct oral treponema, and to relate their presence to periodontal status. Periodontal tissues were evaluated at 4 sites on every tooth except third molars and 76 subjects were classified according to the worst periodontal condition at any one site: Group 1, gingivitis (n = 13); Group 2, early periodontitis (n = 38); and Group 3, advanced periodontitis (n = 25). Subgingival plaque was collected from each half of every tooth evaluated clinically. Spirochetes were identified with phase contrast microscopy and specific treponema were detected immunochemically using monoclonal antibodies to Treponema denticola serovars A-D, T. socranskii subspecies bucalle, T. socranskii subspecies socranskii, and T. pallidum (pathogen-related oral spirochetes, PROS). The counting protocol was conservative and probably underestimated the actual presence of organisms. Spirochetes were found at one or more sites in approximately 60% of subjects in all groups. PROS were found in approximately 40% of subjects in all groups while T. denticola (predominantly serotype B) and T. socranskii (exclusively T. socranskii subsp. buccale) were more frequently observed in Group 2 (roughly 25% for both treponema) than in Groups 1 or 3. Overall, spirochetes were detected in less than 15% of the 4,040 sites examined. Spirochetes were found at more sites of periodontitis (group mean range 20 to 40%) than of gingivitis (6 to 20%), and were only infrequently found at sites of periodontal health (4 to 10%). Spirochetes were identified most often in plaque from around molars and they were usually found in only one of two samples from individual teeth. Results of this study suggest that although spirochetes are most often found associated with periodontitis, their distribution is restricted and most periodontitis sites do not harbor spirochetes.