Subclinical thyroid dysfunction is defined as an abnormal serum thyroid stimulating hormone level and free thyroxine and triiodothyronine levels within their reference ranges. We report here a case of otherwise asymptomatic subclinical hypothyroidism, who progressed to overt hyperthyroidism within a span of one year, with tremors, heat intolerance and fidgetiness. If a patient on levothyroxine for autoimmune hypothyroidism on replacement therapy presents with hyperthyroidism, the possibility of endogenous hyperthyroidism should also be considered.