OBJECTIVE: Patients often lose considerable weight prior to the diagnosis of thyrotoxicosis. Regaining weight with treatment of thyrotoxicosis until hormone levels normalise is expected. This study was aimed to determine whether patients continued to put on weight once they were euthyroid. STUDY DESIGN AND METHOD: The records of 60 consecutive euthyroid patients were studied. All patients were rendered euthyroid on thyrostatic medication alone. Patients on a block and replacement regime, those who developed transient hypothyroidism on treatment or other diagnoses causing weight gain were excluded. RESULTS: The mean age of study group was 46.13 yr (21-73). Male:female ratio was 5:55. 36 (60%) patients had diagnosis of Graves' disease. On initial presentation weight was 67.75 kg (SEM 2.1) with body mass index (BMI) of 25.8. Patients took 6.7 months (mean) to become euthyroid. Mean weight when euthyroid was 71.61 kg (range 46-125). Even after becoming euthyroid, patient continued to gain weight at 3, 6, and 9 months and mean weight gain was 2.04 kg (SD 18.14) at 3 months (p=0.003). This weight gain was not related to patients' age, gender, BMI, duration or dose of treatment required to achieve euthyroidism. Diagnosis of Graves' disease and non-smoking status independently predicted weight gain. CONCLUSION: We have demonstrated that patients with thyrotoxicosis continue to gain weight for at least 6 months even after becoming euthyroid. Patients with Graves' disease were more likely to gain weight compared to others. Smokers gained least weight. Preventing this weight gain warrants further investigation.