BACKGROUND: Road traffic injuries cause 1.2 million deaths worldwide each year. Alcohol consumption increases the risk of traffic crashes, especially fatal crashes. Increased police patrols aim to increase both the perceived and actual likelihood of being caught driving while alcohol-impaired, potentially reducing alcohol-related driving, crashes and injuries. OBJECTIVES: To assess the effects on injuries and crashes of increased police patrols that target alcohol-impaired driving. SEARCH STRATEGY: We searched the Cochrane Injuries Group Specialised Register (5/2006), CENTRAL (The Cochrane Library 2006, Issue 2), MEDLINE (1966 to 5/2006), TRANSPORT (1968 to 5/2006), C2-SPECTR (2/2005), NCJRS (1/1951 to 5/2006), PsycINFO (1872 to 5/2006), Social Science Citation Index (1974 to 5/2006), SIGLE (1980 to 2/2006), Science Citation Index Expanded (1970 to 5/2006), Dissertation Abstracts (1870 to 5/2006), NTIS (1964 to 12/2004), conference proceedings, and reference lists. We contacted authors of eligible studies. SELECTION CRITERIA: Randomized controlled trials, controlled trials, controlled before and after studies, interrupted time series (ITS) studies, and controlled ITS studies evaluating increased police patrols, either alone or combined with other interventions, targeting alcohol-impaired motor vehicle drivers. DATA COLLECTION AND ANALYSIS: Two investigators independently screened citations, extracted data, and assessed quality criteria. We compared intervention and no-intervention geographical areas or time periods. We re-analyzed study data as required. Results are presented narratively. MAIN RESULTS: The 32 eligible studies included one randomized controlled trial, eight controlled before-after studies, 14 controlled ITS studies, six ITS studies, and three studies with both ITS and controlled before-after analyses. Most interventions targeted only alcohol-impaired driving (69%) and included additional interventions such as media campaigns or special training for police officers (91%). Only two studies reported sufficient information to assess study quality completely. Two-thirds of studies were scored 'not adequate' on at least one feature. Five of six studies evaluating traffic fatalities reported reductions with the intervention, but differences were statistically significant in only one study. Effects of intervention on traffic injuries were inconsistent in the six studies evaluating this outcome, and no results were statistically significant. All four controlled studies evaluating fatal crashes reported reductions with the intervention, which were statistically significant in one study. All 12 controlled studies assessing injury crashes reported greater reductions with the intervention, though effects were minimal or not significant in several studies. ITS studies showed less consistent effects on fatal crashes (three studies) and injury crashes (four studies), and effect estimates were typically imprecise. Thirteen of 20 studies showed reductions in total crashes and about two-thirds of these were statistically significant. AUTHORS' CONCLUSIONS: Studies examining increased police patrol programs were generally consistent in reporting beneficial effects on traffic crashes and fatalities, but study quality and reporting were often poor. Methodological limitations included inadequate sample size, dissimilar baseline measures, contamination, and inadequate data analysis. Thus existing evidence, although supportive, does not firmly establish whether increased police patrols, implemented with or without other intervention elements, reduce the adverse consequences of alcohol-impaired driving.