The article presents the results of determining the relationship between morbidity rates and temporary disability (the number of cases of temporary disability per 100 workers, the number of days of temporary disability per 100 workers, the average duration of a case of temporary disability) with the length of service among miners of the main professional groups (drilling rig operators and tunnellers) enterprises for the extraction of iron ore. Causal relationships were established based on the methods of mathematical analysis. In the professional group of drilling rig operators, an increase in the incidence rate with temporary disability due to diseases of the musculoskeletal system and connective tissue with an increase in the length of service in the specialty was revealed; the contribution of the length of service factor to the formation of diseases was 23 %. At the same time, a decrease in morbidity rates with temporary disability due to respiratory diseases and injuries and poisoning was noted. Drivers also showed an increase in morbidity rates with temporary disability for diseases of the musculoskeletal system and connective tissue, and a decrease in morbidity for respiratory diseases and injuries and poisoning. An increase in the incidence rate of tunnellers with up to 10 years of service is also associated with diseases of the musculoskeletal system and connective tissue, and injuries and poisoning. The distribution ranges of morbidity rates among workers with work experience of up to 10 years had statistically significant differences in the number of cases of temporary disability per 100 workers for diseases of the musculoskeletal system and connective tissue among drilling rig operators and tunnellers. The incidence rates of drilling rig operators for this class of diseases are significantly higher. When analyzing the ranges of distribution of indicators of the average duration of a case of temporary disability according to the class of injuries and poisoning among miners with work experience of up to 10 years, it was found that the differences in indicators for drilling rig operators and tunnellers are statistically significant.