Between 1987 and 1990 27 women were observed who professed they did not know they were pregnant until term or until premature contractions set in. The aim of this study was to evaluate obstetric history and pregnancy outcomes and assess defence mechanisms and coping strategies which contribute to negation of pregnancy. In 11 women pregnancy was denied until delivery, five of these had breech presentations. In nine women denial ended between 27 and 36 weeks and in seven women between 21 and 26 weeks of gestation. Three of the four fetal deaths that occurred and two of the three cases of prematurity occurred in the last group. There was no infanticide but one woman delivered her infant alone and concealed. Most women reported irregular, sometimes menstruation-like bleedings during pregnancy, three women had taken oral contraceptives during pregnancy. Few women reported actual symptoms of pregnancy, such as nausea and weight gain. Denial of pregnancy is a heterogeneous condition with different meanings and different psychiatric diagnoses in different women. Stressors (e.g. separation from partner, interpersonal problems etc.) do play an important role as precipitating factors for the development of an adjustment disorder with maladaptive denial of pregnancy. There is a fluid transition between conscious coping strategies and unconscious defence mechanisms.