OBJECTIVE: To evaluate the effectiveness of alcohol-based handrubs (ABH) in reducing acute diarrheal diseases (ADD) and acute respiratory infections (ARI) among children 1-5 years of age in childcare centers with limited tap water. METHODS: This was the first cluster-randomized controlled trial in a developing country. The study took place at 42 childcare centers with sporadic and limited water availability in six towns in Colombia. Participants were randomly assigned to use ABH as a complement to handwashing (intervention arm: 21 centers/794 children); or to continue existing handwashing practices (control arm: 21 centers/933 children). ADD and ARI cases were identified through teacher-reported signs and symptoms of illness. Adverse events were monitored. Hazard ratios (HR) were obtained using Cox proportional hazards multivariate regression shared frailty models. RESULTS: Child-days of surveillance totaled 336 038. Loss to follow up was 14.5%. For both ADD and ARI, there were no differences in hazard ratios during the first trimester of the study. In the second and third trimesters, significant reductions in the risk of ADD were found in the intervention compared to control arm (HR = 0.55, P < 0.001 and HR = 0.44, P < 0.001, respectively). There were also significant risk reductions for ARI in the second trimester (HR = 0.80, P < 0.05) and in the third trimester (HR = 0.69, P < 0.001). No adverse events occurred. CONCLUSIONS: ABH effectively prevent ADD and ARI, and are safe. Colombia's national public health policies for prevention of these diseases should include use of ABH, especially in settings where handwashing with soap and water is limited by water availability.