The Messerklinger technique is a primarily diagnostic endoscopic concept demonstrating that the frontal and the maxillary sinuses are subordinate cavities. Disease usually starts in the nose and spreads through the ethmoidal prechambers to the frontal and maxillary sinuses, with infections of these latter sinuses thus usually being of secondary nature. Standard rhinoscopy and sinus X-rays are frequently not sufficient to demonstrate the underlying causes for chronic or recurring acute sinusitis in the clefts of the anterior ethmoidal sinuses. The combination of diagnostic endoscopy of the lateral nasal wall with conventional or computed tomography in the coronal plane has proven to be the ideal method for the examination of inflammatory disease of the paranasal sinuses. In so doing, diseases and lesions that otherwise might have gone undiagnosed can be identified and consequently treated. Based on this diagnostic approach, an endoscopic surgical concept was developed, aiming for the underlying causes of sinus diseases instead of the secondarily involved larger sinuses. With usually very limited surgical procedures, diseased ethmoid compartments are operated on, stenotic clefts widened and prechambers to the frontal and maxillary sinuses freed from disease. In our experience, there is rarely a need for major manipulations inside the larger sinuses per se. Based on exact diagnosis, the surgical technique used allows a very individualized staging according to the prevailing pathology. In the extreme, a total sphenoethmoidectomy can be performed with this technique, although the true advantage of the technique is that even in cases of massive disease such radical procedures can be avoided. By reestablishing sinus ventilation and drainage via the natural ostia, there is also no need for fenestration of the inferior meatus. The Messerklinger technique can be applied to a wide spectrum of indications, apart from nasal polyposis. The technique has its clear limits as well as its specific problems. Adequate training and experience are required for the surgical approach, as the technique bears all the risks and hazards of all kinds of endonasal ethmoid surgery but has a minimal complication rate in the hands of an experienced surgeon. Results and complications of a series of more than 4500 patients over a period of over 10 years are presented and discussed in detail.