: According to the elemental analysis survey, it is confirmed that the content of silicon (Si) and aluminium (Al) in coarse particles in the ambient air of Erdenet city is the highest (2457 ng/cm2, 1061.72 ng/cm2), and the content of black carbon (BC) is the highest (2699.9 ng/cm2) for the fine particles, respectively. In Orkhon Aimag, 221 new cancer cases were registered in 2023, 20.8 per 10,000 population, and 123 deaths were registered, which decreased by 20 cases from the previous year. Stomach, lung, and oesophageal cancers are the most common. Among the leading causes of diseases, diseases of the respiratory system are led by its prevalence rate of 1536 per 10,000 population, followed by the diseases of the digestive system prevalence rate of 821 per 10,000. Goal: To review the epidemiological tendency of diseases registered in Orkhon aimag between 2006 and 2022. Materials and Methods: The secondary data on outpatient 2006-2022 of Orkhon aimag was collected and analysed. All disease data followed the X International Classification of Diseases classification. The Ethical permission was obtained from the Ethical Committee at the Ach Medical University. All personnel information-related data was removed and no any name and location of personnel data was mentioned in the survey result. Results: In Orkhon Aimag, 524,927 cases of diseases were registered in 2006-2022. Respiratory system diseases were 29.82 percent of total diseases, digestive system diseases were 16.58 percent, genitourinary system diseases were 11.28 percent, cardiovascular system diseases were 10.45 percent, and skin and subcutaneous tissue diseases were 8.38 percent. Chronic heart diseases of rheumatic origin were registered for 11.59 percent of the population aged 50-54, hypertension diseases were registered 12.41 percent, and a steady increase was observed in the age of 20-54. Conclusions
1. When studying the structure of diseases among the population of Orkhon aimag, the respiratory, digestive, and genitourinary system, circulatory system and diseases of the skin and subcutaneous tissue are the first five leading causes of diseases and consisted 76.95% of the total number of diseases. In the study of analyzing the diseases of the circulatory system by age group and diagnosis, cases of ischemic heart disease and high blood pressure are found among children aged 15-19 years. CVD are more common among the population aged 40-54.
2. There is a tendency that skin and subcutaneous tissue diseases to be on the rise among the population.