High-grade differentiated thyroid carcinoma (HGDTC) is a recently recognized entity in the 2022 World Health Organization classification, representing a more aggressive subtype of differentiated thyroid carcinoma. Previously, high-grade features such as increased mitotic activity and tumor necrosis were often overlooked, despite being important independent prognostic factors. Although rare, HGDTC carries significant diagnostic, prognostic, and therapeutic implications. Data remain limited in Indonesia. Methods: This retrospective descriptive study reviewed 565 thyroid carcinoma cases diagnosed at Cipto Mangunkusumo Hospital from 2019 to 2024. Eleven cases (1.9%) met HGDTC criteria. Clinicopathological characteristics, histologic subtypes, Ki-67 proliferation index, molecular alterations, treatment modalities, and clinical outcomes were analyzed. Results: Patients had a mean age of 54.6 years, with a female-to-male ratio of 2.7:1. Papillary thyroid carcinoma was the main type (90.9%), with the tall cell subtype predominating. Mean tumor size was 6.4 cm. Lymphatic invasion, vascular invasion, and extrathyroidal extension were present in 54.5%, 18.2%, and 45.5% of cases, respectively. All tumors showed necrosis. Mean mitotic count was 3 per 2 mm². The Ki-67 index ranged from 5% to 45% (median, 14%). BRAFV600E and TERT promoter mutations were detected in 18.2% and 36.4% of cases, respectively, with co-mutations in 18.2%. Six cases (54.5%) had metastases at time of diagnosis. During a mean follow-up of 20.5 months, one patient (9.1%) developed new vertebral metastases and all patients (100%) remained alive. Conclusions: HGDTC presents with more aggressive characteristics and a worse prognosis. Accurate diagnosis, molecular profiling, and long-term monitoring are essential for optimal management.