The Impact of Informal Relationships Duration upon their Integration LevelThe objective of the study was to compare levels of integration of informal and marital relationships. In the research there was used modified Marriage/Relationship Success Scale constructedon the basis of Marriage Success Scale by M. Braun-Gałkowska (1985). The examination was made for 260 couples (520 persons) including 120 couples (240 persons) living in an informal relationship and 140 marital couples (280 persons). In the examined group of informal relationships as well as in marriages, there prevail homogenic couples – agreeable and satisfied, i.e. with high integration level. It appeared however that extension of the partners’ common life period exerts a negative influence upon the quality of informal relationships, while it does not distort functioning of marriages. This is an evidence for marriages being more stable and constant than informal relationships.