Background: Graves' disease and Hashimoto's thyroiditis are the two autoimmune spectrum of thyroid disease. Cases of conversion from hyperthyroidism to hypothyroidism have been reported but conversion from hypothyroidism to hyperthyroidism is very rare. Although such cases have been reported rarely in the past we are now seeing such conversions from hypothyroidism to hyperthyroidism more frequently in clinical practice. Case presentation. We are reporting three cases of middle aged Asian females who presented with classical symptoms of hypothyroidism and the investigations showed elevated thyroid stimulating hormone with positive thyroid antibodies. Diagnosis of autoimmune hypothyroidism was made and thyroxine replacement therapy was initiated. Patients became asymptomatic with normalization of thyroid stimulating hormone level. After few years they developed symptoms of hyperthyroidism with suppressed thyroid stimulating hormone level. Over replacement of thyroxine was considered and the dose of thyroxine was decreased, but they remain symptomatic. After gradual decrease in the dose of thyroxine it was stopped finally. Even after few months of stopping thyroxine, the symptoms of hyperthyroidism did not improve and the biochemical and imaging modalities confirmed that the patients have developed hyperthyroidism. Anti-thyroid treatment was then started and the patients became symptom free. Conclusion: High index of suspicion should be there for possible conversion of hypothyroidism to hyperthyroidism if a patient with primary hypothyroidism develops persistent symptoms of hyperthyroidism. Otherwise it can be missed easily considering it as an over replacement with thyroid hormone.