The current thesis is a theoretical exploration of how siblings in the childhood impact relational problems in adult lives. This has resulted in a study of psychodynamic lit-erature, including psychoanalytic, object relations and attachment perspectives, to-gether with existing research on the subject. The thesis is divided into two parts. A section on how siblings influence each other in childhood, as well as a section about how sibling relationships in childhood influence relational problems in the adult life.
The section about childhood is necessary, since much literature deals exclusively with siblings during childhood. It is a relatively small and unexplored field, so the answer is not necessarily given in the literature, however, the psychodynamic perspectives despite not directly treating sibling relationships, may still be able to contribute. In the second part of the thesis will be presented, the literature that more directly is aimed towards adulthood .
The first part will include sections on attachment, object relations, sibling order as well as sibling rivalry. The second part will include sections of sibling influence on partner choice, relationship problems , and problems in relation to newborn children.
During the thesis, the different perspectives is discussed against each other.

It was found that sibling relationships seem to have an effect on the individual's inner life that can contribute to relational issues. This is based on the fact that siblings ten-tatively can be considered in some cases to be used as primary attachment figures, secondary attachment figures, transitional objects, internalised as cruel objects and thus affect construction of superego. In some cases rivalry between siblings can have negative consequences, especially if there is an absence of warmth, and especially in the non-functional family where parents are absent and lacing in nurturance. It has also been found, that sibling relationships affect sibling differently, according to their age and birth order, due to different circumstances at birth time and different stages of development.

It has been found that sibling relationships in childhood can influence the choice of a partner, create relationship problems according to unresolved sibling issues, and may cause problems in relation to newborn children, especially if there are more than one.

Many of these conclusions is of general and tentative nature. The main findings are therefore that sibling relationships can have a negative impact on the individual's relationships in adult life. As parental issues can create various kinds of problems, this also seems to be true for sibling relationships. Also, it points to the fact, that this is an area that needs to be explored in depth.