Case study and review of the literature We review the nosology and phenomenology of delusion of pregnancy. Two cases with post partum delusion of pregnancy which can be regarded as a delusion with bizarre content are described. The possible etiological factors particularly aspects of the novel cognitive theories of delusion formation and the hyperprolactinaemia caused by antipsychotic treatment are considered. While discussing the cases with post partum delusion of pregnancy we integrate the false sensory and cognitive processing of the puerperal somatic changes with the motivation theory of delusion formation and with the effect of the cultural environment.