Inconsistent results with regard to adiponectin levels in patients with colorectal cancer (CRC) and adenoma have been reported. To evaluate adiponectin levels in patients with CRC and adenoma, a meta-analysis on studies which compared adiponectin levels in patients with CRC or adenoma with healthy controls was carried out. A literature search was performed through Pubmed, EMBASE, and Science Citation Index Expanded database. Pooled-weighted mean differences and 95% confidence intervals (95%CI) were calculated by using random-effects models. Heterogeneity between studies was assessed using the Cochran’s Q and I2 statistics. A total of 13 studies were identified, which included 2632 cases of CRC or adenoma and 2753 healthy controls. Adiponectin levels were significantly lower in patients with CRC or adenoma compared with healthy controls, with significant heterogeneity [weighted mean differences of −1.51 (95% CI: −2.42 to −0.59; Pheterogeneity<0.001) for CRC and −1.29 (95% CI: −2.01to −0.58; Pheterogeneity<0.001) for colorectal adenoma, respectively]. On stratified analysis of CRC, significant difference in adiponectin levels between patients with CRC and healthy controls was reported only in case–control studies or small sample size studies (n<100), but not in nested case–control studies or large sample size studies (n≥100). In addition, metaregression analysis indicated that study design and sample size partly contributed to the significant heterogeneity (P=0.022 for study design and P=0.018 for sample size, respectively). For colorectal adenoma studies, stratified analysis indicated that sample size was one of the heterogeneous factors. Sensitivity analysis showed that there were no changes in the direction of effect when any one study was excluded. No publication bias was detected. Adiponectin levels are lower in patients with CRC or colorectal adenoma compared with those in healthy controls. Future studies are warranted to clarify the association of adiponectin levels and carcinogenesis of the colorectum.