Purpose: The aim of this study was to systemically review the effect of platform switching on preserving implant marginal bone. Materials and Methods: An electronic search (PubMed and MEDLINE databases) and a hand search of peer-reviewed journals for English-language articles published before June 30th, 2010, were performed. The selected articles included randomized controlled trials (RCTs) and prospective comparative clinical trials with a minimal sample size of 10 subjects and 10 implants followed for at least 1 year after loading. The quality of included RCTs was also assessed. Results: Nine studies met the inclusion criteria; three were prospective comparative studies and six were RCTs. All studies applied either standardized conventional or digital periapical radiographs for the assessment of bone levels. Seven of the nine included articles demonstrated that platform switching was effective in preserving marginal bone around implants. The longest follow-up among these studies was 5 years. Conclusions: Based on the current evidence, the use of abutments with a smaller diameter than their corresponding implant platforms seems to exert beneficial effects on peri-implant marginal bone. Some potential confounding factors, for example, the apicocoronal position of implants in relation to crestal bone, the presence of various implant microtextures, the degree of platform switch, and the reliability of examination methods, should be considered when interpreting the present results. Keywords: crestal bone loss, dental abutments, dental implants, implant design, marginal bone loss, mismatching abutments, platform switch