Parkinson's disease (PD) is a chronic, progressive neurodegenerative disease characterized by bradykinesia, tremor and/ or rigidity, often with gait disturbance and postural instability. In addition to these typical features, patients with PD may experience further problems related to the disease itself or to the medications used to treat it. These comorbid problems include neuropsychiatric conditions (including psychosis, hallucinations, excessive daytime sleepiness, anxiety, depression, fatigue and dementia) as well as problems associated with autonomic nervous system function such as bowel and bladder function. PD can also present in emergency situations with a 'neuroleptic malignant like picture' and acute psychosis. It is not uncommon to see motor fluctuations due to drug interactions and 'withdrawal' symptoms following dose reduction of dopamine agonists. In patients with PD, disturbances of mental state constitute some of the most difficult treatment challenges of advanced disease, often limiting effective treatment of motor symptoms and leading to increased disability and poor quality of life. While some of these symptoms may be alleviated by antiparkinsonian medication, especially if they are 'off-period' related, treatment-related phenomena are usually exacerbated by increasing the number or dosage of antiparkinsonian drugs. Elimination of exacerbating factors and simplification of drug regimens are the first and most important steps in improvement of such symptoms.