There’s a vast list of infectious and non-infectious conditions that can lead to an abnormally elevated body temperature. Non-infectious etiologies include but aren’t limited to: environmental (i.e. heat stroke), drug, transfusion and other hypersensitivity reactions, neoplastic disease, connective tissues disease, vascular disease, and endocrine causes. Infectious etiologies may be broadly grouped into viral, bacterial, or fungal causes. Fever should first be confirmed by use of an accurate thermometer. Clinical evaluation by history and physical is the next step, with further investigation directed according to the severity of illness of the patient and duration of fever. Generally speaking, patients with severe illness or ominous features such as weight loss and those whose fever persists without evident etiology for more than 2-3 weeks should undergo a more detailed clinical, laboratory, and radiologic investigation.