Immune checkpoint inhibitors such as programmed cell death 1 (PD1) and cytotoxic T lymphocyte antigen 4 (CTLA4) monoclonal antibodies have become a notable treatment for various advanced cancers. One of the most common immune-related adverse events (IRAEs) is thyroid dysfunction. This study aimed to investigate the incidence, disease course, and oncologic outcomes of thyroid IRAEs. We performed retrospective review of 222 patients who used immune checkpoint inhibitors for cancer therapy with thyroid function test before and after treatment. Mean (SD) diagnostic age of study patients was 60.6 (11.5) years and men were 67.6% . Lung (34.7%) and stomach (14.4%) were two most common sites of primary cancer. All types of Immune checkpoint inhibitors were included. The prevalence of thyroid IRAEs was 40.5% during median of 2.0 (range, 0.0-22.0) months of follow-up, and median time from baseline to detection of first thyroid dysfunction was 2.0 (range, 0.0-24.0) months. Among 90 patients of thyroid IRAEs, 37 had transient thyroiditis following spontaneous recovery and 36 and 17 of them had subclinical and overt hypothyroidism, respectively. 16 patients who had overt hypothyroidism received levothyroxine therapy, while none of the subclinical hypothyroidism patients needed it. Baseline TSH levels increased from the thyroid IRAE(-) group to the transient thyroiditis, subclinical hypothyroidism and overt hypothyroidism group, in sequence (p for trend =0.014). Within the thyroid IRAE(+) group, the 1st abnormal TSH over 10 uIU/ml was more frequent in overt hypothyroidism than SCH group (42% vs 0%, p <0.001). Finally, patients with overt hypothyroidism showed better overall survival than patients without thyroid IRAEs (14.7 vs 10.0 months, p=0.074). In conclusion, higher baseline TSH and the first abnormal TSH over 10uIU/ml can predict the occurrence of overt hypothyroidism as thyroid IRAEs which was associated favorable oncologic outcomes.