Brain tumors are associated with increased mortality and morbidity and are the most common cancer type in children and young adults. The present review focuses on the interplay between leptin, the most extensively studied adipokine, and the onset, development, and treatment of primary brain and intracranial tumors. The two main mechanisms for increased leptin levels in intracranial tumor survivors, leptin resistance caused by hypothalamic damage, or secondary to obesity, are discussed. The contradicting mechanistic observations on leptin being able to both promote tumorinogenesis (e.g., in gliomas) as well as inhibit it (e.g., in adenomas) are also reported. Additionally, the relevant current and future clinical applications, including most notably the proposed use of serum leptin measurements for non-invasive brain tumor diagnostics, are also reported.