Purpose: A systematic review of the available literature to assess the effects of time to loading of implants on treatment outcomes. Methods: PubMed search strategies identifying clinical trials on implant prosthetics, combined with searching of a personal library and reference lists from included studies, resulted in 1,882 titles published before May 1, 2005. Two independent reviewers appraised the titles and abstracts and identified 187 papers that seemed to focus on the effects of time to loading on treatment outcomes in clinical trials. These papers were retrieved and critically appraised in full text. A set of predefined inclusion and exclusion criteria were applied. All trials (randomized and nonrandomized clinical trials, prospective and retrospective) were included in the review if both an experimental and a control group were adequately described, if the implants had been followed for at least 1 year, and if the sample contained at least 5 patients. Results: Twenty-two papers, published between 1990 and 2005 described the influence of time to loading on implant treatment success. Seven trials were randomized controlled trials, 13 were prospective with concurrent controls, and 2 were retrospective with concurrent controls. The general impression of the papers was that (1) the methodologic rigor of the trials was often not very strong, (2) the reported treatment outcomes were mostly surrogate rather than patient-centered, and (3) the follow-up times were relatively short. Statistical comparisons between subgroups were considered inappropriate because of the heterogeneity of trials. Data from 19 trials reporting different patient follow-up periods between 1 and 10 years suggest that the overall performance was not significantly different between immediate or early loaded implants versus implants using a conventional loading period. Conclusion: Within the limitations of the study populations in the papers appraised in this systematic review, although the average outcome was in favor of delayed loading, there are no indications that immediate or early loading cannot be a safe procedure. Palabras clave: early loading, immediate loading, oral implants, osseointegration, prosthodontics