Primary lymphocytic hypophysitis is an autoimmune disease characterized by lymphocytic infiltration of the pituitary gland, with a higher incidence during late pregnancy and the postpartum period. It causes glandular destruction, mass effect and symptoms such headache, visual field defects, ophthalmoplegia and symptoms of hypopituitarism. We report a 38-year-old postpartum woman who, after giving birth presented decreased left visual acuity associated with a non ictal headache. Magnetic resonance imaging demonstrated a sellar mass associated with decreased free thyroxine and cortisol levels. Suspecting a primary lymphocytic hypophysitis, she was treated with prednisone 60 mg/day and hormonal replacement therapy. One month later, size of the pituitary gland decreased, and the visual field defect improved. Steroidal treatment was maintained for 36 months and progressively tapered. After two years of follow-up, the imaging studies show a normal sized pituitary gland.