Endoscopy is a routine diagnostic and important therapeutic method. Gastroscopes are used to examine the upper part of the digestive system while colonoscopes are used to examine the lower part of the digestive system. Examination with a colonoscope or colonoscopy is a diagnostic method of examination in gastroenterology that allows examination of the entire colon. The most important process that needs to be complete before performing a colonoscopy examination is adequate cleansing of the intestines, as it ensures the successful completion of the examination in accordance with the expertise and good teamwork of the medical staff. The Boston scale is still the best and most reliable because it evaluates all parts of the intestine in detail as well as determines their readiness for examination. This scale divides the colon into three segments: the right side, the transverse colon, and the left side of the colon. Research objective: To define quality parameters for colonoscopy and to determine what factors affect on adequate preparedness of intestines in patients referred to colonoscopy at Zadar General Hospital. Test subjects and methods: A retrospective analysis has been done on the data from hospital system (BIS) of the Zadar General Hospital. It included patients who did the colonoscopy in time period from 1.1.2020. until 31.12.2021. The test includes the number of subject , their age and the degree of bowel cleansing. During that we used the Boston scale for intestines preparedness. Results: In the study 3593 patients participated. The male gender occupies a slightly higher percentage compared to the female gender. The age group of 66 to 75 years is the most common group that undergoes colonoscopy and the best cleaning results are recorded in the left colon