In the following, a case of mother-adult son incest is described and e
xplained from a psychoanalytical viewpoint. Two theories are put forwa
rd: (a) Mother-son incest may occur as a defence against psychosis, an
d (b) the incest represents an unconscious search for triangulation, a
process in which external authorities (such as, for example, a court
of law) may function as surrogates for persons who have been missed in
the pre-oedipal past. It is therefore possible to understand mother-s
on incest symbolically as an indicator of pre-oedipal needs of the son
and of the mother's longing for the absent partner. The incest is, ho
wever, not only a cry for help; it is also to be regarded as an attemp
t to solve the problem for both people involved. Looked at in this way
, new ways of understanding and new possibilities for therapy emerge.