The posterior pituitary high signal (PPHS) seen on MRI of the sella in normal individuals probably reflects antidiuretic hormone (ADH) granules stored in the posterior pituitary lobe (PPL). We present a case with anorexia nervosa, high serum ADH, and oliguria who underwent three cerebral MR studies over the course of treatment. The first MR examination showed absence of PPHS and early enhancement of the PPL on dynamic MRI. In subsequent MR examinations PPHS became evident in concomitance with clinical improvement. This case suggests that PPHS changes may reflect reaccumulation of ADH granules and that dynamic MR of the PPL may be useful for assessing the vascularity of the PPL and/or the reversibility of its function.