Objective Analyses of bladder cancer mortality in the Black Foot Disease (BFD) endemic area of southwest Taiwan conducted by Morales et al. showed a discontinuity in risk at 400 μg/L arsenic in the drinking water in a stratified analysis and no discontinuity in a continuous analysis. As the continuous analysis presentation had been used by both the NRC and the EPA to assess the carcinogenic risk from arsenic ingestion, an explanation of the discontinuity was sought. Methods Review of 40 years of published health studies of the BFD-endemic area of SW Taiwan showed that earlier publications had limited their cancer associations with arsenic levels in artesian well waters and that the reports of Morales et al., NRC, and EPA failed to do so. Underlying data for the Morales et al. study were obtained from the appendix to the NRC report. Bladder cancer mortality rates were calculated from case counts and person-years of observation for each study village. Villages were categorized by water source according t Objective Analyses of bladder cancer mortality in the Black Foot Disease (BFD) endemic area of ​​southwest Taiwan conducted by Morales et al. Showed a discontinuity in risk at 400 μg / L arsenic in the drinking water in a stratified analysis and no discontinuity in a continuous analysis. As the continuous analysis presentation had been used by both the NRC and the EPA to assess the carcinogenic risk from arsenic ingestion, an explanation of the discontinuity was sought. SW Taiwan showed that earlier publications had limited their cancer associations with arsenic levels in artesian well waters and that the reports of Morales et al., NRC, and EPA failed to do so. Underlying data for the Morales et al. Study were obtained from the appendix to the NRC report. Bladder cancer mortality rates were calculated from case counts and person-years of observation for each study village. Villages were categorized by water source according t