Twenty eight patients with hyperthyroidism complicating their pregnancies were seen at the Obstetrics and Gynaecology Department, University Hospital, Kuala Lumpur, Malaysia in a six-year period. All patients were treated with antithyroid drugs, carbimazole being the mainstay of treatment. The incidence of the disease was 0.9 per 1000 births and was similar with other series. No cases of fetal goitre were noted. The mean birth weight was 2952 g; there was no significant difference in the birth weight of term live births in patients treated with carbimazole alone or carbimazole combined with propranolol.