The pathophysiologic process and clinical factors that contribute to the development of treatment resistance in schizophrenia are not well defined. This article describes data indicating that treatment resistance may evolve over the course of the patients' illness and maturational development. Data from multiepisode patients suggest that early effective intervention with clozapine can prevent treatment resistance. Early identification of patients with signs of treatment resistance is vital. Treatments must be effective and prevent relapse. At the first indication that a patient may be developing resistance (e.g., the emergence of extrapyramidal symptoms or increases in negative symptomatology) or may not be complying with treatment, clozapine therapy should be considered.