BACKGROUNDDrinking water at US Marine Corps Base Camp Lejeune, North Carolina, was contaminated with trichloroethylene and other industrial solvents from 1953 to 1985.METHODSA cohort cancer incidence study was conducted of Marines/Navy personnel who began service and were stationed at Camp Lejeune (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__N=154,821) or Camp Pendleton, California (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__N=163,484) between 1975 and 1985 and civilian workers employed at Camp Lejeune (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__N=6,494) or Camp Pendleton (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__N=5,797) between October 1972 and December 1985. Camp Pendleton's drinking water was not contaminated with industrial solvents. Individual-level information on primary invasive cancers and in situ bladder cancer diagnosed between 1996 and 2017 was obtained from 54 US cancer registries. Proportional hazards regression was used to calculate adjusted hazard ratios (aHRs) comparing cancer incidence between the Camp Lejeune and Camp Pendleton cohorts, adjusted for sex, race, education, and rank (or blue-collar work), with age as the time variable. Precision of aHRs was evaluated using the 95% confidence interval (CI) ratio (CIR).RESULTSCancers among Camp Lejeune Marines/Navy personnel and civilian workers totaled 12,083 and 1,563, respectively. Cancers among Camp Pendleton Marines/Navy personnel and civilian workers totaled 12,144 and 1,416, respectively. Compared with Camp Pendleton, Camp Lejeune Marines/Navy personnel had aHRs __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__≥1.20 with CIRs __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__≤3 for all myeloid cancers (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.24; 95% CI: 1.03, 1.49), acute myeloid leukemia (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.38; 95% CI: 1.03, 1.85), myelodysplastic and myeloproliferative syndromes (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.68; 95% CI: 1.07, 2.62), polycythemia vera (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.41; 95% CI: 0.94, 2.11), and cancers of the esophagus (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.27; 95% CI: 1.03, 1.56), larynx (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.21; 95% CI: 0.98, 1.50), soft tissue (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.21; 95% CI: 0.92, 1.59), and thyroid (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.22; 95% CI: 1.03, 1.45). Lymphoma subtypes mantle cell and marginal zone B-cell and lung cancer subtypes adenocarcinoma and non-small cell lung cancer also had aHRs __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__≥1.20 with CIRs __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__≤3. Compared with Camp Pendleton, Camp Lejeune civilian workers had aHRs __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__≥1.20 with CIRs __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__≤3 for all myeloid cancers (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.40; 95% CI: 0.83, 2.36), squamous cell lung cancer (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.63; 95% CI: 1.10, 2.41), and female breast (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.21; 95% CI: 0.97, 1.52) and ductal cancer (__-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__HR=1.32; 95% CI: 1.02, 1.71).CONCLUSIONIncreased risks of several cancers were observed among Marines/Navy personnel and civilian workers exposed to contaminated drinking water at Camp Lejeune compared with Camp Pendleton. https://doi.org/10.1289/EHP14966.