The article is devoted to the analysis of the ways of translating the Polish indefinite pronoun «coś» into Russian. The purpose of the research is to determine the dependence of the translator’s decision on the semantic load of the pronominal lexeme and its surrounding context. The Polish-Russian Parallel Corpus created at the University of Warsaw served as the material for the research. As the research has shown, the Russian indefinite pronoun «chto-to» can be used as an equivalent for «coś», as well as a non-referential pronoun «chto-nibud’», a negative polarity pronoun -«libo», weakly defined pronouns and pronouns of obscurity. Other translation solutions are possible in several contexts, they lead to the preservation, weakening, or complete rejection of the semantics of uncertainty.