Schizophrenia is a severe and disabling psychiatric illness involving primary symptoms of psychosis (hallucinations, delusions, disordered thinking and behavior). Unfortunately, as many as 30% of patients respond poorly to standard antipsychotic medications and are considered to have treatment resistant schizophrenia (TRS). Neuropsychological impairment is an important clinical feature of schizophrenia, as cognitive deficits predict poor treatment response, daily functioning, and disability. However, very little is known about cognitive functioning in the clinically complex subset of patients with TRS. The aims of this project are therefore to investigate the severity, pattern, and variation in cognitive functioning among individuals with TRS, and to determine whether cognitive difficulties predict treatment response and functioning. This will be achieved by analyzing clinical and neuropsychological data that has been collected on TRS patients who have been treated within the BC Psychosis Program since 2012. Findings using this unique dataset will have a direct impact on shaping assessment and treatment strategies, improving prognosis and ability to predict functioning, and improving clinical decision-making and planning.