There is current disagreement over whether men and women respond differently to typical or atypical antipsychotic medications. This study reanalyzed a large international clinical trial of olanzapine (Olz) compared with haloperidol (Hal) to test for sex differences in treatment response, controlling for illness chronicity and menopausal status. We hypothesized that women would show a greater response to either medication than men, particularly among first admission, premenopausal women. DSM-III-R schizophrenia inpatients (700 women and 1295 men) were randomly assigned to a 6-week trial of Olz vs. Hal. Longitudinal random effect models were used to test for interactions of sex with medication, chronicity and menopausal status on treatment response. Findings showed that women on olanzapine had a greater drop in overall symptomatology by week 4 than any other group, and their level of symptomatology remained lower throughout the 6-week trial. The sex differences in treatment response in olanzapine compared with haloperidol were, in part, dependent on chronicity and, in women, menopausal status. That is, first episode women on haloperidol exhibited an increase in symptomatology over the 6-week trial compared to their male counterparts, while multiply hospitalized women had a better treatment response on haloperidol than their male counterparts. Women on olanzapine had a significantly better treatment response than men, regardless of chronicity. Finally, premenopausal women had a significantly better treatment response than postmenopausal women, regardless of treatment and chronicity.