It has been indicated that COVID-19 is related to many endocrinological abnormalities. The aim of this study is to demonstrate whether there is an impact of COVID-19 and COVID-19 vaccines on development of subacute thyroiditis (SAT). This retrospective single-center study includes individuals with SAT who were diagnosed between March 2020 and August 2021. Patients were evaluated for a recent Covid-19 history and SARS-CoV-2 vaccination. SAT was diagnosed based on the clinical presentation and laboratory tests; including thyroid function tests, sedimentation rate, C-reactive protein, and thyroid ultrasound. SARS-CoV-2 PCR results of patients with past COVID-19 were obtained from the Ministry of Health electronic patient data system. Type, number, and dates of vaccine doses were recorded for each participant. A total of 31 patients were included in the study. Six patients (19.4%) were diagnosed with SAT following a COVID-19 vaccination schedule. Four patients with SAT had received two inactive (CoronaVac) + one dose of mRNA vaccines (Pfizer-BioNTech). The other 2 patients had received either two doses of inactive vaccine or two doses of mRNA vaccine. Five patients were diagnosed with SAT after the second dose of the vaccine. The median interval between last vaccination dose and diagnosis of SAT was 25.8 days. In one patient, SAT developed 28 days after the mRNA vaccine. Seven patients (22.6%) were diagnosed with SAT after COVID-19 disease. The median interval from the diagnosis of COVID-19 disease to SAT was 27.3 days. All cases of post-COVID-19 and post-vaccination SAT patients exhibited similar clinical presentation and findings to idiopathic SAT. Covid-19 itself and Covid-19 vaccines might let a tendency to development of subacute thyroiditis. This study has to be supported by further studies.