A 37 year old woman presented to A&E with symptoms of hyperemesis gravidarum. She was 9 weeks pregnant, in her third pregnancy. It was noted that her calcium level was 3.13mmol/l, PTH 12.1 pmol/l, vitamin D 42nmol/l. She was treated with IV fluids and discharged with endocrine follow up. The endocrine and obstretric teams arranged for an urgent review on the antenatal ward the next week. Calcium was still raised at 3mmol/l. She was admitted overnight for antiemetics and IV fluids until calcium was 2.79mmol/l. She had been recently diagnosed with likely primary hyperparathyroidism at a different hospital but had only undergone part of the necessary investigations before moving to a new area. Hypercalcaemia likely exacerbated her nausea and was itself exacerbated by the dehydration from vomiting. She required weekly blood tests and IV hydration as calcium levels rose quickly between admissions. The option of parathyroid surgery was discussed as it was difficult to maintain the calcium in a normal range with hydration alone. Ultrasound of the parathyroids showed two likely adenomas in the left inferior and right inferior parathyroid glands. The patient agreed to surgery in the second trimester. Hypercalcaemia in pregnancy is associated with complications for both the mother and the foetus. The mother can develop hyperemesis gravidarum, nephrolithiasis, osteoporosis, pancreatitis, as well as having a higher risk of pre-eclampsia. The foetal complication rate has been shown to be up to 80%, including growth restriction, preterm delivery and miscarriage. Postpartum, up to 50% of neonates have transient hypocalcaemia. If medical management is insufficient in pregnancy, parathyroid surgery can be considered and is usually performed in the second trimester due to the potential impact on organogenesis in the first trimester and risk of preterm labour in third trimester. These decisions require a multidisciplinary approach and discussion with the patient regarding risks and benefits of medical and surgical treatments.