The study presents a case of a 64-year-old patient with diagnosed Parkinson’s disease and coexisting REM sleep disorders (RBD) confirmed in a polysomnographic examination. In this patient, the use of supplementary therapy – quetiapine (50mg/daily) – due to psychotic disorders, resulted in speech disorders with sensory-motor mixed aphasia type. Aphasia occurred on the fourth day after beginning the treatment with atypical neuroleptic. In MRI examination of the head, no “fresh” cerebral ischemia was found. No focal status epilepticus was reported in the video EEG trial. Results. Complete cure occurred after discontinuation of quetiapine administration. Conclusions. Due to the above, the side-effects of quetiapine treatment were assumed as the cause of focal neurological disorders.