Application of clinical endoscopic Nd:YAG laser (lambda = 1.06 micron) therapy has been introduced in 1975. It is suitable to stop all kinds of gastrointestinal bleeding with a primary success rate of 94% (1144/1212). Compared to surgical results a reduction in mortality rate has been achieved. These results have been confirmed worldwide in routine clinical application and in controlled trials with selected patients. Potential bleeding lesions such as Osler haemangiomas and angiodysplasias can be sealed. Recanalization of inoperable obstructed oesophageal and gastric carcinoma by laser vaporization to relieve dysphagia and subsequently endoscopic iridium after loading irradiation show a medium survival time of 7.4 months. Preoperative recanalization of obstructed colorectal carcinoma to relieve ileus or subileus allows preoperative peroral bowel lavage and total colonoscopy to find synchronous cancers and polyps and to perform primary resections without intraoperative colon lavage. Sessile benign neoplastic polyps can be resected curatively by Nd:YAG laser vaporization. Recanalization of peptic stenosis and anastomotic scar stenosis can be performed.