We report a 63-year-old male who was referred to nuclear medicine unit for thyroid scanning with provisional diagnosis of Graves' disease. The patient presented to endocrinology clinic few days before referral with clinical features of heart failure and bilateral exophthalmos, with no history of previous thyroid surgery or anti-thyroid medication. Clinically there awas diffuse enlargement of the right thyroid lobe with no definite nodules and no palpable left lobe. His thyroid hormonal profile revealed evidently elevated free T3 and free T4 [12.9 pmol/L (N: 3.1-6.8) and 38.4 pmol/L (N:12-22) respectively] associated with markedly suppressed serum TSH level (< 0.005mIu/ml). Antimicrosomal antibodies (thyroid peroxidase antibodies) were positive with negative antithyroglobulin antibodies. Tc99m pertechnetate thyroid scan revealed diffuse enlargement of the right lobe with intense homogenous tracer uptake pattern, and more intense tracer uptake in its mid substance due to thicker thyroid tissue rather than true nodule. The upper and lower poles showed intense uptake, more than would be expected for such thinner parts of the lobe. On the other hand the left lob was not functionally suppressed. It is of average size with evidently less tracer uptake in a homogenous pattern, again it harbors no nodules (Fig1). The total thyroid uptake level was 11.5%, the right lobe uptake was 9.9 % while left lobe uptake was 1.6% (Fig1). High resolution thyroid ultrasound (Fig2) revealed average size of the left lobe (14x12x34mm) with decreased echogenicity and no increase in vascularity. On the other hand, the right lobe is enlarged (22x24x46) with coarse texture and no nodules. The combined scintigraphic and sonographic data exclude the presence of toxic nodule occupying the whole right thyroid lobe. The patient was diagnosed as Graves' disease affecting only the right thyroid lobe (unilateral Graves' disease).