OBJECTIVES: To compare antipsychotic medication patterns, side-effects and concomitant medication usage for olanzapine and haloperidol patients in a cross-sectional analysis of the GEO observational study. METHODS: GEO is a 2-year prospective naturalistic combined in- and outpatient observational study in Germany. 646 adult schizophrenia patients treated with either olanzapine (N=416) or haloperidol (N=230) were enrolled in the study and quarterly observations on the disease course, resource consumption and quality of life are made during the follow-up period. RESULTS: More olanzapine patients were newly switched to their current treatment (27% vs. 18% within 2 weeks before enrolment) or switched more than 2 weeks but less than 3 months before enrolment (19% vs. 12%). Patients switched within the last 3 months had spent more days in hospital during the last year than patients treated for more than 3 months (29 days vs. 15 days). In the 12 months prior to being enrolled in the study, olanzapine patients had spent more days in hospital due to schizophrenia compared with the haloperidol patients (23 vs. 19 days). Olanzapine patients had lower incidence of treatment related EPS side-effects (27% vs. 70%), whereas other treatment side-effects (mainly related to adipositas and depression) were reported more frequently for olanzapine patients (29% vs. 9%). A smaller proportion of olanzapine patients received concomitant antipsychotic medication (31.0% vs. 48.7%) and EPS medication (1.6% vs. 20.5%) compared with haloperidol patients. The concomitant use of antidepressants (24.8% vs. 5.4%) and anxiolytics (24.0% vs. 13.4%) were more common for olanzapine compared with haloperidol patients. CONCLUSIONS: At time of enrolment in the GEO observational study, more olanzapine patients were recently switched to their current treatment, and had spent more days in hospital. Additional antipsychotic medication use was more common for haloperidol patients. Olanzapine patients had fewer treatment side-effects and lower usage of concomitant side-effects medication.