Thyroid carcinoma is not uncommon in patients with hyperthyroidism. However, the risk of malignancy in patients with autonomously functioning nodules continues to be underestimated in clinical practice, possibly due to the belief of rare co-existence of a "hot" nodule and thyroid carcinoma. We present hereby a man with hyperthyroidism due to a thyroid toxic adenoma, who was subjected to surgery and incidentally found to have a papillary thyroid microcarcinoma on the contralateral thyroid lobe. By reviewing the literature, incidental thyroid carcinoma in patients subjected to thyroidectomy for a hyperfunctioning nodule, both within and out of the nodule is not a rare event. However, the incidental finding of thyroid carcinoma out of a hyperfunctioning nodule is not adequately reviewed in the literature.