Purpose: To retrospectively assess implant stability quotient (ISQ) values in patients who were followed up between 1998 and 2014 and to evaluate any correlations between ISQ and clinical parameters, such as change in marginal bone level (MBL). Materials and Methods: A total of 173 participants (65 men and 108 women; age range 21 to 85 years) and 383 implants were included. Implant location, MBL, and ISQ were recorded at surgery and at various recall times for statistical analysis. Mixed-model analysis was applied to evaluate the impact of clinical and demographic variables (time, implant location, patient gender) on ISQ and the correlation between ISQ and MBL. The level of significance was set at P .05. Results: Of the 21 failed implants, 20 failed within 1 year of functional loading, resulting in a 10-year cumulative implant survival estimate of 95%. The failed implants had lower ISQs at surgery (52.3 ± 7.03) and baseline (52.5 ± 4.20) when compared to surviving implants (63.0 ± 10.74 at surgery and 62.3 ± 8.30 at baseline), and the difference was statistically significant at surgery (P .05). The mean ISQs generally increased over time, but there were various patterns of changes between implants when grouped according to patient gender and implant location. There was no statistically significant correlation between the changes in ISQ and MBL (P = .211), despite an inverse relationship. Conclusion: Low initial ISQ values may help to identify implants at higher risk of failure. There may be various patterns of change over time in addition to an overall increase in ISQ values. Both similar and contradictory findings were found when compared to earlier literature, and a correlation between resonance frequency analysis and MBL change could not be identified. Despite limitations, the present study provides an overview of the clinical performance of RFA based on long-term clinical data.