Clinical diagnosis of parkinsonian syndrome is reasonably easy, but the distinction between idiopathic Parkinson's disease (IPD) and other parkinsonian syndromes (Secondary parkinsonisms and "Parkinsons plus") may be very difficult particularly in early cases. A correct diagnosis is not only important for counselling and management of patients but also in conducting pharmacological and epidemiological studies. A critical analysis of the diagnosis criteria of IPD, based on the pathological verification, is discussed from recent data of literature. Without any validated and available criteria from functional imaging or molecular biology, the most effective diagnostic criteria remain on the clinical range; the five most effective criteria are resting tremor, rigidity, bradykinesia, asymmetry at onset and marked levoDOPA responsiveness. The diagnosis of IPD should be periodically reassessed along the course of its natural history.