This was an observational case-control study carried out in the Department of Biochemistry, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka jointly with the 'Thyroid and Endocrine Clinic' of the same institution during the period of January 2002 to December 2002. Sixty-five (65) newly diagnosed hyperthyroid patients between 20-60 years of age were studied, where forty-five (45) were Graves' disease and twenty (20) were TMNG (Toxic multinodular goiter) patients. Thyrotoxicosis was diagnosed by history, clinical examination and biochemical investigations- FT4, TSH, and Radioactive iodine uptake (RAIU) test. Thirty (30) age and sex matched healthy subjects were taken as control. The mean age was 33.02+/-9.24 years in Graves' disease and 37.55+/-9.49 years in TMNG. Female predominance observed in both the diseases. Glucose intolerance was found in 72.3% of thyrotoxic patients, which is much higher than European population. Our study showed Diabetes mellitus (DM) in 11% of Graves' disease patients. The incidence of DM in Graves' disease was slightly higher in our population. Incidence of DM in TMNG in our study was much lower (5%) than that of Graves' disease (11%) but the incidence of IGT (Impaired glucose tolerance) in TMNG was more (85%) in relation to Graves' disease (54%). Percentage of RAIU was more marked in Graves' disease than TMNG. There is a significant positive correlation (p<0.05) between plasma glucose and FT4 in Graves' disease. Glucose intolerance is frequently found in Thyrotoxic patients.