Objectives: To assess the beneficial or harmful effects of systemic prophylactic antibiotics at dental implant placement versus no antibiotic/placebo administration and, if antibiotics are of benefit, to find which type, dosage and duration is the most effective. Data sources: The Cochrane Oral Health Group's Trials Register, CENTRAL, MEDLINE and EMBASE were searched and several journals were handsearched with no language restriction up to January 2008. Review methods: Randomised controlled trials (RCTs) with a follow up of at least 3 months comparing the administration of various prophylactic antibiotic regimens versus no antibiotics to patients undergoing dental implant placement were eligible. Screening of studies, quality assessment and data extraction were conducted in duplicate. Missing information was requested. Outcome measures were: prosthesis and implant failures, postoperative infections and adverse events (gastrointestinal, hypersensitivity, etc.). Results: Two RCTs were identified: one comparing 2 g of preoperative amoxicillin versus placebo (316 patients) and the other comparing 2 g of preoperative amoxicillin + 500 mg four times a day for 2 days versus no antibiotics (80 patients). The meta-analyses of the two trials showed a statistically significant higher number of patients experiencing implant failures in the group not receiving antibiotics: RR = 0.22 (95% CI 0.06 to 0.86). The number needed to treat (NNT) to prevent one patient having an implant failure is 25 (95% CI 13 to 100), based on a patient implant failure rate of 6% in patients not receiving antibiotics. The other outcomes were not statistically significant, and only two minor adverse events were recorded, one of which was in the placebo group. Conclusions: There is some evidence suggesting that 2 g of amoxicillin given 1 hour preoperatively significantly reduce failures of dental implants placed in ordinary conditions. It remains unclear whether postoperative antibiotics are beneficial, and which is the most effective antibiotic. It might be recommendable to suggest the use of one dose of prophylactic antibiotics prior to dental implant placement. Keywords: antibiotics, dental implants, prophylaxis, randomised controlled clinical trial, systematic review