A 39-year-old gravida 8, para 6 woman at 34 weeks of a twin gestation was admitted to the antenatal ward with severe agitation and restlessness. She had a history of unstable bipolar disorder for which she was treated with lithium. Before admission she had been under close supervision by psychiatric and obstetric teams and lithium levels had been stable. However, an acute deterioration in renal function secondary to ureteric obstruction resulted in toxic plasma lithium levels and associated clinical features. An emergency caesarean section was carried out under general anaesthesia. We provide a review of the current literature including: the pharmacology of lithium, the effects of lithium on fetus and mother, and the current guidelines for management of lithium treatment during pregnancy. Lithium is prescribed relatively rarely during pregnancy. We aim to increase awareness about the issues involved in the management of women receiving lithium during pregnancy.