Several studies have suggested arsenic may target important tumor-suppresser genes and disrupt cell cycle control and influence bladder cancer risk. In a large, population-based case-control study we evaluated whether there was heterogeneity in the arsenic-bladder cancer risk relationship by tumor expression of p16 and Rb. Tumor tissue from bladder cancer cases was assembled as tissue microarrays and examined for expression. Cutoff values used to define negative/positive staining were based on the distribution of the percentage of positive cells in cases. Data on cumulative arsenic from drinking water were used to evaluate the relationship between arsenic and bladder cancer by immunophenotype (p16-/p16+,Rb-/Rb+), in 424 cases and 1287 controls, using polytomous logistic regression. Our results show that the association between increasing cumulative arsenic and bladder cancer risk was only apparent among patients with p16+ or Rb+ tumors. We observed a strong monotonic association between risk and increasing cumulative arsenic intake (Quartile2-4 vs. Quartile1, ORp16+ =1.36, 1.47, 1.85, p-trend=0.004 and ORRb+ =1.51, 1.56, 1.94, p-trend=0.007). No association between cumulative arsenic and risk among patients with p16- or Rb- bladder tumors was apparent (p-heterogeneity by subtype=0.0325 for p16 and 0.0551 for Rb). This heterogeneity was not evident by stage or grade. Our data suggest a low frequency of homozygous deletion of CDKN2A (the gene that encodes p16), as well as inactivating mutations of RB1 in arsenic-induced bladder cancer, pointing to an alternate mechanism. Increased p16 expression may be indicative of hypermethylation of CDKN2A, an intensively studied mechanisms for arsenic-induced carcinogenesis. Our data provide additional evidence linking arsenic exposure and bladder cancer risk and point to alterations of the cell cycle as the relevant pathway, although the precise mechanisms need further evaluation in additional experimental and human studies.