In psychology the Medical Model views mental illness as coming from an underlying physiological or biological cause. Clinicians using this model view psychological issues as symptoms of a biological disease or brain injury. There is heavy focus on genetics and neuroanatomy.
A clinician practicing the medical model would first identify the patient's symptoms. Symptoms can be grouped together in order to identify a possible syndrome and give the patient a diagnosis. For example, Schizophrenia can be easily diagnosed using the medical model because it is a biological disease. The clinician would note the symptoms (delusions, hallucinations) and other biological considerations (family members with schizophrenia- there is a genetic predisposition) and make a diagnosis of schizophrenia. Treatment options (medication, therapy) would then be considered.