Studies have found increased bladder cancer risks associated with high levels of arsenic in drinking water, but little information exists about risks at lower concentrations. Ecologic studies in Argentina have found increased bladder cancer mortality in Córdoba Province, where some wells are contaminated with moderate arsenic concentrations. This population-based bladder cancer case-control study in two Córdoba counties recruited 114 case-control pairs, matched on age, sex, and county, during 1996-2000. Water samples, particularly from wells, were obtained from subjects' current residences and residences in the last 40 years. Statistical analyses showed no evidence of associations with exposure estimates based on arsenic concentrations in drinking water. However, when well-water consumption per se was used as the exposure measure, time-window analyses suggested that use of well water more than 50 years before interview was associated with increased bladder cancer risk. This association was limited to ever smokers (odds ratio = 2.5, 95% confidence interval: 1.1, 5.5 for 51-70 years before interview), and the possibility that this association is due to chance cannot be excluded. This study suggests lower bladder cancer risks for arsenic than predicted from other studies but adds to evidence that the latency for arsenic-induced bladder cancers may be longer than previously thought.