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Aim: To study the prevalence of thyroid dysfunction and its association with disease severity in hospitalized patients of coronavirus disease-19 (COVID-19). Methods: In this retrospective cohort study, thyroid function tests (TFT) of 236 hospitalized patients of COVID-19 along with demographic, comorbid, clinical, biochemical and disease severity records were analysed. Patients were divided into previous euthyroid or hypothyroid status to observe the effect o f prior hypothyroidism on the severity of COVID-19. Results: TFT abnormalities were common. Low free T3 (FT3), high thyroid-stimulating hormone (TSH) and low TSH were seen in 56 (23.7%), 15 (6.4%) and 9 (3.8%) patients, respectively. The median levels of TSH (2.06 vs 1.26 mIU/mL, P = 0.001) and FT3 (2.94 vs 2.47 pg/mL, P < 0.001) were significantly lower in severe disease. Previous h ypothyroid status (n = 43) was associated with older age, higher frequency of comorbidities, higher FT4 and lower FT3. TFT did not correlate with markers of inflamm ation (except lactate dehydrogenase); however, FT3 and TSH negatively correlated with outcome severity score and duration of hospital stay. Cox regression analysis showed that low FT3 was associated with severe COVID-19 (P = 0.032, HR 0.302; CI 0.101–0.904), irrespective of prior hypothyroidism. Conclusions: Functional thyroid abnormalities (low FT3 and low TSH) are fre quently seen in hospitalized patients of COVID-19. Although these abnormalities did not correlate with markers of inflammation, this study shows that low FT3 at a dmission independently predicts the severity of COVID-19.