The GSTM1 null/GSTT1 null genotype was associated with an increased CRC risk in the overall analysis (− − vs. + +: OR = 1.42, 95% CI: 1.17–1.73, I2 = 68.6%; − − vs. + −: OR = 1.37, 95% CI: 1.00–1.88, I2 = 73.0%; − − vs. (+ −) + (− +): OR = 1.26, 95% CI: 1.05–1.51, I2 = 70.4%; − − vs. (+ −) + (− +) + (+ +): OR = 1.26, 95% CI: 1.09–1.46, I2 = 69.0%). This evidence concerns the gene GSTM1 and colorectal carcinoma.