Diagnosis is the process of identifying a disease by its signs, symptoms and results of various diagnostic procedures. It can also be the conclusion reached through that process.

Typically, someone with abnormal symptoms will consult a physician, who will then obtain a history of their present illness and examine them for signs of disease. The physician will formulate a hypothesis of likely diagnoses and in most cases obtain further testing to confirm or clarify the diagnosis before proceeding to render treatment.

The list of most likely and possible diagnoses based on available information is called a differential diagnosis; the final diagnosis is only arrived at after other diseases on this list have been eliminated through further investigations or consultations.

See also: nosology, ICD, Diagnosis-related group.