Multidrug resistance 1 (MDR1) gene encodes the ATP-dependent cellular efflux pump P-glycoprotein (P-gp) which efflux of a variety of substances across the membrane. P-gp could serve a role in cancer etiology based on its physiological role of protecting cells from xenobiotics or metabolites. The C3435T (rs1045642) polymorphism of the MDR1 gene which could influence the P-gp expression and function have been implicated in the cancer risk. However, the results from the published studies on the association between this polymorphism and cancer risk are conflicting. To drive a more precise estimation of this association, we performed a meta-analysis of 39 case-control studies, including a total of 9,265 cancer cases and 13,502 controls. We used odds ratios (ORs) with their 95% confidence intervals (CIs) to assess the strength of the association. Overall, individuals with the MDR1 3435TT genotype were associated with an increased cancer risk than those with the CC (OR = 1.29, 95% CI: 1.10-1.51) or CT/CC (OR = 1.18, 95% CI: 1.04-1.34) genotypes, similar to the CT or CT/TT compared with the CC genotype. In the stratified analyses, the increased risks were more pounced among hematologic malignances (OR = 1.27, 95% CI: 1.10-1.46, P (heterogeneity) = 0.415), breast cancer (1.42, 1.04-1.94, 0.018), renal cancer (1.77, 1.28-2.46, 0.307), Caucasians (1.21, 1.07-1.38, 0.000) and population-based studies (1.20, 1.05-1.36, 0.000) in a dominant model. The results suggested that the MDR1 C3435T polymorphism may contribute to cancer risk.