Objective: Dental implants and peri-implant tissue are susceptible to disease conditions that may lead to implant loss. The objective of the present study was to describe teeth and implant surroundings as well as clinical health indices and oral microbiologic parameters. Method and Materials: A group of 83 adults (42 men and 41 women) were enrolled in the study. Clinical assessments of dental implants and contralateral natural teeth included dental plaque, gingival inflammation, and bleeding on probing. Microbiologic assessments included bacterial culture, light and phase contrast microscopy, and DNA probe hybridization for a panel of 14 target microorganisms. Clinical and microbiologic data were compared by paired t test and ANOVA. P .05 was considered statistically significant. Results: The Plaque Index for the implants was 1.85 ± 0.47, whereas the score for natural teeth was significantly higher, 2.15 ± 0.52. Compared to the samples obtained from the dental implants, the samples from natural teeth demonstrated significantly higher total bacterial cell numbers (P .05). Consistent with the clinical measures of dental plaque, significantly higher numbers of oral bacteria, including aerobic and anaerobic bacteria, were found in dental plaque samples from teeth (aerobic 5.648 ± 0.512, anaerobic 6.243 ± 0.535, P .0001) compared to implants (aerobic 5.430 ± 0.541, anaerobic 5.917 ± 0.523, P .0001). In addition, there were significantly higher numbers of anaerobic (6.243 ± 0.535 and 5.917 ± 0.523, P .0001) than aerobic (5.648 ± 0.512 and 5.430 ± 0.541, P .008) bacteria for samples from teeth and implants, respectively. Conclusion: Clinical and microbiologic analyses provide consistent findings that suggest differences in quantity of plaque and bacterial species between teeth and dental implants. For long-term treatment success, the importance of plaque control and oral hygiene of both periodontal and dental implant therapy is emphasized. Schlagwörter: clinical health indices, dental implants, microbiologic parameters, natural teeth, oral biofilms