Objectives:
The objective of the study was to assess the prevalence and incidence of tardive dyskinesia in patients treated with olanzapine during the follow-up period of 20 months.

Methods:
It was a prospective, observational, non-interventional study under naturalistic conditions, without a control group. The evaluation of the severity and presence of tardive dyskinesia was performed with the Abnormal Involuntary Movement Scale and research criteria by Schooler and Kane.

Results:
The study included 573 patients (woman 43,3%) with the diagnosis of schizophrenia (ICD-10), the mean age of 41.8 (± 12) years. The mean dose of olanzapine was 15.9 (±4.2) mg. The prevalence of tardive dyskinesia was 16.4%. The cumulative incidence assessed in the group of 479 patients was 6.47%. The annual incidence was 3.9%. An increased risk of tardive dyskinesia was observed in smokers – RR of 1.99 (CI 0.88-4.49), those taking higher doses of olanzapine 1.57 (CI 0.91-2.7) and in those who used polytherapy: 3.55 (CI 1.43-8.82). Only in the case of polytherapy a multidimensional analysis confirmed that this factor had a significant influence on the risk of tardive dyskinesia (p=0.006).

Conclusions:
The study demonstrated high (16,4%) prevalence of tardive dyskinesia, and the annual incidence (3,9%) comparable to the results of a meta-analysis by Corell et al. In the case of olanzapine in monotherapy the annual incidence was lower (1.96%) but the use of antipsychotics in polytherapy more than tripled the risk of tardive dyskinesia.