AbstractBackground:Evidence linking arsenic in drinking water to digestive tract cancers is limited. We evaluated the association between arsenic levels in groundwater and gallbladder cancer risk in a case–control study (2019–2021) of long-term residents (≥10years) in two arsenic-impacted and high gallbladder cancer risk states of India—Assam and Bihar.Methods:We recruited men and women aged 30 to 69 years from hospitals (73.4% women), with newly diagnosed, biopsy-confirmed gallbladder cancer (N = 214) and unrelated controls frequency-matched for 5-year age, sex, and state (N = 166). Long-term residential history, lifestyle factors, family history, socio-demographics, and physical measurements were collected. Average-weighted arsenic concentration (AwAC) was extrapolated from district-level groundwater monitoring data (2017–2018) and residential history. We evaluated gallbladder cancer risk for tertiles of AwAC (μg/L) in multivariable logistic regression models adjusted for important confounders [Range: 0–448.39; median (interquartile range), T1–0.45 (0.0–1.19); T2–3.75 (2.83–7.38); T3–17.6 (12.34–20.54)].Results:We observed a dose–response increase in gallbladder cancer risk based on AwAC tertiles [OR = 2.00 (95% confidence interval, 1.05–3.79) and 2.43 (1.30–4.54); Ptrend = 0.007]. Participants in the highest AwAC tertile consumed more tubewell water (67.7% vs. 27.9%) and reported more sediments (37.9% vs. 18.7%) with unsatisfactory color, odor, and taste (49.2% vs. 25.0%) than those in the lowest tertile.Conclusions:These findings suggest chronic arsenic exposure in drinking water at low-moderate levels may be a potential risk factor for gallbladder cancer.Impact:Risk factors for gallbladder cancer, a lethal digestive tract cancer, are not fully understood. Data from arsenic-endemic regions of India, with a high incidence of gallbladder cancer, may offer unique insights. Tackling ‘arsenic pollution’ may help reduce the burden of several health outcomes.