Visceral obesity is an important factor that increases the risk of complications after colorectal cancer surgery. As calculating visceral fat is difficult and time-consuming, more practical fat measurements that are not time-consuming have been introduced. This study aimed to investigate the effects of perirenal fat thickness on postoperative complications and prognosis in patients undergoing surgery for colorectal cancer. Perirenal fat thickness was measured from the dorsal aspect of the left kidney on preoperative computerized tomography of patients who underwent surgery for colorectal cancer. The effects of perirenal fat thickness on postoperative complications were investigated. Diagnostic test performance was examined using the Roc Curve test to determine the cutoff value for the perirenal fat thickness values according to the complication findings of the patients. The cutoff value of perirenal fat thickness was found to be above 25.1, according to the presence of complications in the patients. Those with a perirenal fat thickness greater than 25.1 mm were considered to have high perirenal fat thickness values, and those with a low perirenal fat thickness value were considered low. Multivariate analysis revealed that increased perirenal fat thickness is an independent risk factor for postoperative complications. We believe that perirenal fat thickness measurement, as an indicator of visceral fat volume, can be used to identify patients at high risk of developing complications after colorectal cancer surgery. This may change the disease management and affect the patient information process.