Colorectal cancer represents the third cause of cancer. Since its detection in due time is important resolution, appropriate monitoring is mandatory. The present study deals with the relationship between colorectal cancer and renal function, as well as other associated risk factors. Chronic kidney disease (CKD) represents a risk factor of cancer, both in non-dialysed patients and especially in dialysed patients and in patients with renal transplant. It can get aggravated with cancer in general and particularly with colorectal cancer, partly related to the toxins that cannot be appropriately eliminated because of renal functional disturbances. At the same time, immunosuppressive therapy used for treating glomerular or secondary nephropathies represents an important risk factor of cancer. Some patients with colorectal cancer were found to present also impaired renal function, a fact whose significance is still little known. The object of the present paper is an analysis of the case records of a clinic of gastroenterology on the relationship between colorectal cancer and renal functional impairment. We found in the patients with colorectal cancer under study a glomerular filtration rate (GFR calculated with the EPI formula) of < 60 ml/min/1.73m2 in 31/180 patients, respectively 17.22% of the cases, a value that is similar to that in specialised literature. We also analysed associated risk factors that could be related to renal function impairment in these patients: age, gender, anaemia, diabetes mellitus and hypertension. These could represent, together with the colorectal cancer of the investigated patients, risk factors affecting on the one hand renal function, and on the other hand, potentially increasing the risk of cancer. Correction of these risk factors would have beneficial effects on patients. The relationship between renal functional impairment, respectively CKD, and colorectal cancer is to be regarded from the point of view of complex reciprocity: the impairment of the renal function is a factor of risk of colorectal cancer and colorectal cancer can influence renal function of these patients. This report of reciprocity based on important pathogenic mechanisms also interrelates with factors of risk consecutive to both renal function impairment and colorectal cancer.