This retrospective study aims to identify factors that contribute to either a poor or excellent treatment result in implant-overdenture treatment. A total of 375 implants, in an equal number of patients were included in the study. A clinical examination was performed by 2 observers. Gingival health and oral hygiene were assessed and additional complications were noted, including implant loss. 2 outcome variables, STATUS1 and STATUS2, were constructed that were different with respect to treatment outcome, representing a poor and an excellent result, respectively. Patient variables such as age, gender, medical status and prosthetic history were collected pre-operatively with a questionnaire. Life table analyses were used to test subsets of patient and treatment variables for differences in survival distribution, both for poor or excellent results. With regard to predictors of poor results; implants in the upper jaw were associated with a poorer outcome than those placed in the lower jaw (p = 0.01). When more than 2 implants were placed, the quality of survival was also impaired (p = 0.03). Interestingly, implants in patients with a self-proclaimed history of tooth loss due to periodontitis appear to have a far poorer treatment outcome than implants placed in patients without such a history (p = 0.01). No other variables could be related to a poor result after 3 years. None of the variables could predict an excellent treatment outcome.