Subacute thyroiditis stands out along with suppurative thyroiditis as painful, being rare conditions. Since its description by Fritz De Quervain, it is considered a viral or post-viral disease, however it has been reported after the application of influenza and hepatitis vaccines. A 51-year-old man presented with 3 days after the application of the second dose of the messenger RNA vaccine BTN162b2 (Pfizer-BioNTech) against COVID-19, presented general symptoms in addition to neck pain, exacerbated by palpation of the thyroid gland. The laboratory tests demonstrated the systemic inflammatory response, with suppression of thyroid-stimulating hormone and an increase in free thyroxine. A thyroid ultrasound with a low uptake pattern confirmed the diagnosis of subacute thyroiditis in temporal relation to his vaccination history. After 3 months of management with nonsteroidal anti-inflammatory drug, beta-blockers, and gastric protectors, his symptoms reverted and his thyroid hormone profile normalized.