Links between the CHEK2 1100delC heterozygote and breast cancer risk have been extensively explored. However, both positive and negative associations with this variant have been reported in individual studies. For a detailed assessment of the CHEK2 1100delC heterozygote and breast cancer risk, relevant studies published as recently as May 2012 were identified using PUBMED and EMBASE and selected using a priori defined criteria. The strength of the relationship between the CHEK2 1100delC variant and breast cancer risks was assessed by odds ratios (ORs) under the fixed effects model. A total of 29,154 cases and 37,064 controls from 25 case-control studies were identified in this meta-analysis. The CHEK2 1100delC heterozygote was more frequently detected in cases than in controls (1.34% versus 0.44%). A significant association was found between CHEK2 1100delC heterozygote and breast cancer risk (OR=2.75, 95% CI: [2.25, 3.36]). The ORs and CIs were 2.33 (95% CI: [1.79, 3.05]), 3.72 (95% CI: [2.61, 5.31]) and 2.78 (95% CI: [2.28, 3.39]) respectively in unselected, family, early-onset breast cancer subgroups. The CHEK2 1100delC variant could be a potential factor for increased breast cancer risk in Caucasians. However, more consideration is needed in order to apply it to allele screening or other clinical work.