44 years old lady was referred to Endocrinology Clinic with history of secondary amenorrhea and hyperprolactinaemia (7800), that responded to Cabergolin treatment, which was discontinued after 2 months due to side effects (headaches). There was no galactorrhea or visual field defects. MRI Pituitary initially reported as Empty Sella. Her prolactin levels rose further along with headach after she discontinued Cabergoline (and refused alternatives). She eventually agreed for night time dose of bromocriptine. She initially tolerated low dose of Bromocriptine with biochemical response and monthly menstrual periods returned. After a few months, she discontinued Bromocriptine due to insomnia and lethargy. Cabergoline was restarted but she stopped it when she became pregnant. She had an early miscarriage and was subsequently started on Quinagolide. Serum Prolactin kept fluctuating and was attributed to variable compliance. Repeat MRI pituitary was requested when her Prolactin rose upto 9600 which revealed no evidence of micro or macro adenoma in pituitary fossa which was described as mainly fluid filled consistent with Arachnoid cyst. Short Synacthen Test was normal. We present a rare case of hyperprolactinaemia in which imaging was consistently negative for Pituitary adenoma but evidence of Arachnoid cyst and Empty sella.