The prevalence of thyroid cancer is steadily rising and the fortuitous discovery of a thyroid nodule is a frequent situation for the clinician. The clinical importance is the need to exclude thyroid cancer. In this article we present the initial work up and treatment options for differentiated thyroid cancer. Initial diagnosis is done with a dosage of thyroid stimulating hormone and a fine needle aspiration guided by ultrasonography, which permits classification of the lesion and guides the choice of treatment.