The purpose of the study is to analyze the impact of informal employment on formation of structural deficiency of mandatory medical insurance in Russia. The methodology is based on the balance sheet method for estimating informal employment by comparing Rosstat data on average annual and average listed number of employees across economic sectors in 2023, followed by calculation of fiscal losses using established mandatory medical insurance contribution rate of 5.1%. The study revealed direct budget losses of the Federal mandatory medical insurance Fund at the rate of 127.1 billion RUB annually, with highest concentration in trade (36.4 billion RUB), construction (19.3 billion RUB) and manufacturing (15.8 billion RUB). It is established that structural deficiency of the Federal mandatory medical insurance Fund and chronic under-financing of health care (4.5% of GDP) against in average of over 9% in OECD countries are directly related to scale of informal sector. The conclusions testify the necessity of comprehensive reformation of the system? including diversification of sources of the Federal mandatory medical insurance Fund, measures of legalization of labor relations and restoration of confidence to institutions of social insurance as conditions of financial sustainability.

informal employment, social insurance system, mandatory medical insurance, fiscal losses, informal economics, social contributions, health care financing.