Purpose: This systematic review evaluated treatment outcomes for mandibular mini-implant- retained overdentures (MMIOs) in terms of (1) implant survival rate, (2) peri-implant marginal bone loss, (3) prosthodontic maintenance and complication occurrence, and (4) patient satisfaction. Materials and Methods: Pertinent literature published in English before October 12, 2015 was identified using a MEDLINE and EMBASE search strategy and hand searching of relevant journals. Inclusion and exclusion criteria were applied to the titles and abstracts and subsequently to the full text of included studies. A total of 16 articles were included, from which qualitative and quantitative data were extracted for analysis. Results: Of the 16 evaluated articles, 5 were randomized controlled trials, 8 were prospective studies, and 3 were retrospective studies. The follow-up time range from implant placement was 1 to 6 years, and only four studies included more than 3 years of follow-up. The mini-implant survival rate ranged from 86.9% to 100%. Mean marginal bone resorption was 0.28 to 1.2 mm after 1 year of loading. Of the 16 studies, 5 reported prosthodontic maintenance and complications, and all included studies showed significant improvement in patient satisfaction. Conclusion: Despite the limitations of this systematic review, particularly the short follow-up periods, the results suggest that MMIOs showed predictable results regarding implant survival rates, marginal bone resorption, and patient satisfaction.