The article represents the mathematical model of medical service of servicemen, who do not take medical advice themselves. The model based on the semi-Markov stochastic process theory. Dependence is established of working-capacity index on periodicity of clinical examinations at different intensities of diseases, quality of diseases diagnosticating, duration of health recovering and realization of prophylactic measures. Existence of optimal period between clinical examinations, with maximal rate of working-capacity index, is shown.