Recent evidence suggests that schizophrenia patients taking atypical antipsychotic medications may perform better on some tests of cognitive function than those treated with older antipsychotics. The current study compared the effects of quetiapine and haloperidol on measures of executive function, memory and attention. Subjects were 58 stable outpatients with schizophrenia (DSM III-R) who received a battery of cognitive tests as part of a randomized, double-blind, multi-site clinical efficacy study conducted by AstraZeneca Pharmaceuticals. Cognitive assessments were conducted prior to randomization when patients were receiving < or =30 mg haloperidol or equivalent (mean: 9.2mg/day haloperidol equivalents), and again after 24 weeks of fixed-dose treatment with either quetiapine 600 or 300 mg/day or haloperidol 12 mg/day. Analyses of covariance with planned comparisons were used to compare scores on cognitive measures at the end of 24 weeks by treatment group with baseline cognitive function scores used as covariates. Patients receiving quetiapine 600 mg/day improved to a greater extent than patients receiving haloperidol on overall cognitive function (p<0.02). Specific differences were found for executive function (Verbal Fluency Test, p<0.04), attention (Stroop Color Word Test, p<.03) and verbal memory (Paragraph Recall Test, p<0.02). Treatment group differences were not solely due to benztropine use, medication side effects, or changes in symptomatology. Treatment with quetiapine at higher doses (600 mg/day) relative to haloperidol appears to have a positive impact on important domains of cognitive performance that have been found to predict role function and community outcomes in patients with schizophrenia.