Considerable numbers of foreigners migrated to Poland since the late 1980s. Citizens of the former USSR, and especially from neighbouring Ukraine, predominated. The aim of our article is to illustrate on the example of immigration from Ukraine and of Polish-Ukrainian marriages the relation between short-term labour immigration, the phenomenon of mixed marriages and settlement immigration to Poland. Using official statistics we demonstrate that foreigners married to Polish citizens constitute a considerable part of settlement immigration to Poland. In describing the process of mixed marriages formation we take Gary Becker's economic approach to human behaviour. We assume that the possibility to live in Poland, provided by Polish partners to their Ukrainian partners, constitutes a non-market trait of Poles. In addition, our analysis reveals that young age and a high level of education of Ukrainian partners are their non-market traits, which play an unquestionable role in the analysed matchmaking process. On the basis of qualitative research conducted among Polish-Ukrainian marriages, we also demonstrate that Ukrainian partners had often experienced temporary migration to Poland (prior to their marriages to Poles).