Data on divorces are gathered by the Czech Statistical Office and thus widely accessible and well known, but much less information is available about the stability of unmarried cohabitations. This paper focuses on the differences between marriage and unmarried cohabitations in terms of their stability. The authors study the impact of various factors on the stability of marriages and unmarried cohabitations taking into account the different socio -demographic indicators. To explain this phenomenon they use various theoretical approaches emphasizing different factors of partnership instability (from socializing factors to premarital cohabitation, values, education and gender, to factors based on the theory of rational choice). The analysis identified factors that operate in the same manner within both marriages and unmarried cohabitations (e.g. children in the partnership, experience with the previous partnership break-ups) as well as factors that play a different role in the stability of marriages and unmarried cohabitations (e.g. education, duration of partnership, generation). The paper is based on quantitative data from the survey ‘Life-course 2010’, which included 4010 respondents. The authors used the event history approach in their analysis which enabled them to track the dependences of the variables in time., Marta Vohlídalová, Hana Maříková., 1 graf, 1 tabulka, Poznámky na str. 14-15 (14), Biografické poznámky o autorkách článku na str. 15, Obsahuje bibliografii, and Resumé o klíčová slova anglicky na str. 3