Periodic psychosis in relation to the menstrual cycle phases has been reported but its pathogenesis not yet known. We report a case of a 28 year old female with schizoaffective disorder since 18 years old. She was diagnosed with polycystic ovary syndrome (PCOS) 3 years later and was noted to have distinct psychotic episodes that coincided acutely with her premenstrual period. Peculiarly she exhibited delusions of pregnancy during her psychotic episodes. This was followed by near resolution with the end of menstruation. This case sheds light on this atypical presentation of psychosis in female patients as well as its potential aetiology.