Hyperthyroidism can occur secondary to gestational trophoblastic disease. The clinical and biochemical data of four women who had hyperthyroidism secondary to gestational trophoblastic disease was analyzed. The parity ranged from primi to gravida four and the period of amenorrhoea from six weeks to sixteen weeks. Three women had vomiting, two had bleeding per vaginum and two had tachycardia and minimal thyromegaly. The betahCG was more than 5,00,000 mlu/ml in all the cases. Three women required treatment for the hypermetabolic status and one woman had biochemical hyperthyroidism. Two of them had molar pregnancy, one had partial mole and one had persistent trophoblastic disease.