A retrospective follow-up study was undertaken to assess the clinical condition, complications, and prosthodontic aftercare of two different implant systems over a long period. Thirty-six patients treated with a total of 135 ITI type F endosseous implants, and 37 patients treated with the transmandibular implants and a total of 146 transmandibular posts, were studied during a mean follow-up period of 70 months and 44 months, respectively. The choice of implant type was mainly influenced by a change in financial support by the National Health Insurance Company in The Netherlands in 1987. Cumulative success rates were calculated using the Kaplan-Meier product limit method. In the analysis, the risk for failure of the implants was adjusted for differences in mandibular bone height. There were no differences between the two treatment groups with regard to age, gender, period of edentulousness, and mandibular bone height. During the follow-up period, plaque, bleeding, and hyperplasia scores demonstrated no significant differences between the two groups. The ITI type F group showed significantly more recession, and the transmandibular implant group demonstrated significantly increased Periotest values. After adjusting for differences in bone height, patients treated with ITI type F implants had a lower risk of failure (relative risk, 0.55; 95% confidence interval 0.32 to 0.95). However, neither of the implant systems fulfilled Albrektsson's criteria of success. Keywords: follow-up, implant, overdenture, superstructure