This PhD thesis addressed clinical situations during follow-up in patients with an uncomplicated diverticulitis and patients who had undergone curative surgery for colorectal cancer. It tried to determine the necessity of endoscopic follow-up by means of colonoscopy to rule out a malignant neoplasm of the large intestines in patients who were treated conservatively for uncomplicated diverticulitis. Results showed there is no higher risk of developing colorectal cancer after an uncomplicated diverticulitis. In the second part, different clinical results after curative surgery for colorectal cancer were investigated. In order to optimise and improve quality management during follow-up, increased pre-operative tumour markers, colorectal obstruction, and oncological outcome after anastomotic leakage and postoperative colonoscopies was investigated in a single central institution.