Background: Construction workers are frequently exposed to various types of injury-inducing hazards. A number of injury prevention interventions have been proposed, yet the effectiveness of these is uncertain. Objectives: To assess the effects of interventions for preventing injuries among workers at construction sites. Search strategy: We searched the Cochrane Injuries Group's specialised register, CENTRAL, MEDLINE, EMBASE, PsycINFO, OSH-ROM (including NIOSHTIC and HSELINE), EI Compendex. The reference lists of relevant papers, reviews and websites were also searched. The searches were not restricted by language or publication status. All databases were searched up to June 2006. Selection criteria: Randomized controlled trials, controlled before-after studies and interrupted time series of all types of interventions for preventing fatal and non-fatal injuries among workers at construction sites. Data collection and analysis: Two authors independently extracted data and assessed study quality. For interrupted time series, we reanalysed the studies and used an initial effect, measured as the change in injury-rate in the year after the intervention, as well as a sustained effect, measured as the change in time trend before and after the intervention. Main results: Five interrupted time series studies met the inclusion criteria. Three studies evaluated the effect of regulations, one evaluated a safety campaign, and one a drug-free workplace program on fatal or non-fatal injuries compared to no drug-free workplace program. The overall methodological quality was low. The regulatory interventions did not show either an initial or sustained effect on fatal or non-fatal injuries, with effect sizes of 0.69 (95% confidence interval (CI) -1.70 to 3.09) and 0.28 (95% CI 0.05 to 0.51). The safety campaign did have an initial and sustained effect, reducing non-fatal injuries with effect sizes of -1.82 (95% CI -2.90 to -0.75) and -1.30 (95% CI -1.79 to -0.80) respectively. The drug-free workplace program did have an initial and sustained effect, reducing non-fatal injuries compared to no intervention, with effect sizes of -6.74 (95% CI -10.02 to -3.54) and -1.76 (95% CI -3.11 to -0.41) respectively. Authors' conclusions: The vast majority of technical, human factors and organisational interventions which are recommended by standard texts of safety, consultants and safety courses, have not been adequately evaluated. There is no evidence that regulations for reducing fatal and non-fatal injuries are effective. There is limited evidence that a multifaceted safety campaign and a multifaceted drug program can reduce non-fatal injuries in the construction industry.