A method and apparatus for providing an on-site diagnosis of a subject to determine the presence and/or severity of a concussion is provided. The method includes placing an electrode set coupled to a handheld base unit on the subject's head, acquiring brain electrical signals from the subject through the electrode set, processing the acquired brain electrical signals using a signal processing algorithm stored in a memory of the base unit, determining the presence and/or severity of a concussion from the processed signals, indicating the presence and/or severity of a concussion on the handheld base unit, and determining a course of treatment for the subject based on the indication.