In the health technology assessment it is crucial to define the perspective of the analysis. When the societal perspective is chosen it is necessary to include all the costs incurred by the society, also the costs of lost productivity resulting from absence of sick employees from work or their reduced efficiency at work. The aim of this article is to present the notion of indirect costs, their importance in health technology assessment and the methods of calculation. The economic literature has been reviewed for the state of knowledge on indirect costs. Three methods of calculation are described: human capital method, friction cost method or health state valuation. Indirect costs in Western European countries can amount to more than half of total costs attributed to the illness and its treatment. In the literature there is no consensus regarding the proper method of indirect costs calculation. It is necessary to conduct further theoretical and empirical research in the area of indirect costs and enhance discussion among Polish pharmacoeconomists.