Aim of the study:
The issue of relationships with siblings in early adulthood is relatively rarely explored by researchers. The purpose of the presented research was to characterize this relationship and to define its importance for the interpersonal function of young adults.

Subject or material and methods:
The study included 100 participants at an average age of 27.08 years (SD=4.38). In the surveyed group 60% were women (n=60) and 40% men (n=40). The following methods were used in the study: Adult Siblings Relationships Questionnaire – Short Form, the Empathic Sensitiveness Scale and Humour Styles Questionnaire.

Results:
The results of the research revealed that sisters have the relationships with siblings based on Warmth, achieve higher average results in Empathic Care and Personal Distress and lower average results in Self-defeating humour than brothers. Relational variables with predictive value for empathy and humour styles were identified in both groups. In the group of brothers, they explained a higher percentage of variance in results.

Discussion:
The presented results indicate that the quality of relationships with adult siblings significantly influences selected dimensions of interpersonal functioning.

Conclusions:
The results of the study broaden the psychological knowledge of family psychology and have application aspect.