BACKGROUND Diabetes insipidus is uncommon in pregnancy. Despite physiological modifications in hydroelectrolytic balance during normal pregnancy, the capacity of the kidney to concentrate urine is preserved, partially due to lower vasopressin secretion. METHODS A young woman developed diabetes insipidus during the third trimester of normal pregnancy. The disease regressed totally after delivery. However, magnetic resonance imaging revealed a persistent expansive intrasellar image with a high-intensity signal. CONCLUSIONS Onset of diabetes insipidus is usually rapidly progressive in pregnancy. Occurring generally during the third trimester in normal pregnancies, diabetes insipidus is generally well tolerated and responds to dDAVP, usually without pituitary abnormally, and regresses after delivery. Two types are distinguished: partially latent diabetes insipidus occurring during pregnancy and due to a central rather than nephrogenic origin; and excessive vasopressinase activity leading to diabetes insipidus usually associated with liver anomalies and high frequency of pre-eclampsia. During normal pregnancy, the size of the anterior pituitary increases and the normal high-intensity signal in the posterior pituitary seen on MRI usually regresses or disappears. In diabetes insipidus, the posterior pituitary hypersignal image generally disappears, reflecting reduced vasopressin storage. Few observations of diabetes insipidus occurring during pregnancy have been reported with morphological explorations. Most have described a "normal" aspect of the pituitary, specifically in the post partum period. In our patient, the weak vasopressin response to the end of water restriction at post partum when the diabetes insipidus symptoms had disappeared would suggest partial central diabetes insipidus revealed by pregnancy. Other pathologies involving this region could also be involved due to the unusual and persistent sellar image, with an expansive process showing a high intensity signal on MRI. An asymptomatic craniopharyngioma cyst was hypothesized and would be more compatible with the observed symptoms.