Hyperemesis gravidarum is defined as excessive nausea and vomiting in pregnancy, which incapacitates the pregnant lady from her daily routine activities. Thyroid dysfunction is very common during pregnancy, more so in south east Asia. It can either be preexisting or pregnancy aggravated thyroid disorders. It has been seen that there is an association between hyperemesis gravidarum and thyroid dysfunction in pregnancy. This could be due to the elevated beta HCG levels.The most common disorder noted is called transient gestational hyperthyroidism, which seldom requires treatment. The aim of this study was to study and characterize thyroid dysfunction in patients with hyper emesis gravidarum. The objectives of this study were: 1. to determine the percentage of thyroid dysfunction in antenatal mothers diagnosed with hyperemesis gravidarum. 2. To determine the percentage of hyperemesis gravidarum patients with euthryoid state, hyperthyroidism and hypothyroidism. 3. To determine the percentage of patients with hyperthyroidism with hyperemesis , who required treatment. Methods: An in house clinical analytical one time observational study was done on 25 antenatal mothers, who were admitted to the father medical college obstetric inpatient unit with hyperemesis gravidarum. The clinical details and investigation reports of the patients were noted as per a semi structured performa. Each woman was examined for clinical signs of thyroid disease and underwent investigations including hemoglobin, urine ketone, urine microscopy and thyroid function tests (TFT) as well. The data was analysed using SPSS software. Results: Five patients (20%) had biochemical hyperthyrodism (suppressed thyroid stimulating hormone and increased free tetraiodothyronine index), 4 percent had hypothyroidism (subclinical and overt) and 19 patients (76%) had normal thyroid tests. Among the four percent (5) hypothyroid patients, two had tested positive for anti thyroid autoanitbodies (Anti TPO). These were positive with mean ± SD 145±73.1 IU/mL.Four percent of patients with hyperemesis,had symptomatic and bio chemical hyperthyroidism that required antithyroid therapy (PTU).ninety six percent of hyperemesis patients however did not require any therapy for hyperthyroidism. Conclusion: In our study thyroid dysfunction was 24% in subjects with hyperemesis gravidarum.The clinical features of thyrotoxicosis in women with hyperemesis gravidarum are usually absent. A few patients however may have clinically evident thyrotoxicosis. The thyrotoxicosis of hyperemesis gravidarum usually resolves spontaneously within several weeks as the vomiting disappears.In rare instances; due to the severity of clinical presentation patients may require treatment with PTU. A follow up study on patients with hyperemesis who develop hyperthyroidism requiring therapy, will probably give more conclusive evidence.