Endoscopic diagnosis and therapy of colorectal carcinomas comprise their early and late forms. In adenomas with invasive carcinoma, polypectomy is at the same time a complete therapy if the site of removal is histologically free from any tumour. In case of established invasion of the submucous lymphatic vessels and a low degree of differentiation subsequent segmental resection is generally recommended. Advanced carcinomas do not present any special problem in respect of identification by endoscopy. Biopsy can also be performed at the same time. In case of inoperable tumours, endoscopy offers by means of the YAG laser an additional palliative treatment method for extending the lumen or haemostasis.