The Blacky Picture Test was administered to a sample of 12 pairs of male MZ twins, aged 17 to 19 years, and to an equal number of singletons. A score for 30 factors was assigned to each protocol. By comparing the scores of the two groups using the Mann-Whitney U test, only one significant difference emerged, relative to the factor concerned with positive identification and fraternal relationship. Twins chose the sibling figure as the identification object significantly less often than singletons did. A more qualitative elaboration was undertaken in order to interpret this result. From the final data, the pre-cariousness of the sense of identity in the twins comes out indirectly in their passive and conformistic acceptance of the paternal model. It would seem that the twin is induced by his relationship with his cotwin, seen as the origin of this uncertainty as to his own identity, to adhere closely to the paternal image.