Objectives: To provide a comprehensive description of consumptive hypothyroidism syndrome (CHS), a severe form of hypothyroidism that occurs due to the high expression levels of thyroid hormone inactivation enzyme type 3 deiodinase (D3) in tumors. Study Design: Case report and systematic review. Results: A 7-month-old girl with a diagnosis of massive hepatic hemangioendotheliomas was treated with high doses of thyroid hormones and tumor-directed chemotherapy with vincristine. The tumor displayed excellent response, and euthyroid status was regained. A systematic review on the databases PubMed/Medline and Embase was performed, using the term “Consumptive AND “Hypothyroidism.” From the 33 selected references, we extracted 42 case reports of CHS: 36 children and 6 adults. The laboratory profile at diagnosis displayed high TSH and low T4 and T3 serum levels. The serum reverse T3 and D3 activity levels were high in all patients tested. In children, 97% had vascular tumors, whereas in adults 33% were vascular tumors, 33% fibrous tumors, and 33% gastrointestinal stromal tumors. The conservative treatment was predominant in children, while in adults all cases were treated with surgery. Death occurred in 16% of children and 33% of adults. Conclusions: CHS is a rare form of hypothyroidism that occurs in children and adults, usually linked to hepatic vascular tumors. The condition is associated with high lethality. Prompt diagnosis, followed by high-dose thyroid hormone replacement and tumor-directed therapy are the keys to optimize outcomes.