At the time when Parkinson’s Disease is diagnosed in a patient, roughly two-thirds of dopaminergic neurons of substantia nigra are already degenerated. The onset of the disease must, therefore, be much earlier. This work deals with early diagnosis and early preventive treatment which may sustain the process underlying the disease. By use of psychometric, kinesiologic, physiologic, histologic, biochemical, endocrinologic, pharmacologic and imaging techniques, including positron-emission tomography and brain mapping, specialists tried to focus on new diagnostic criteria. New methods including psychometric evaluation, apparative measurement of movement, analysis of peripheral blood and urinary constituents have supplemented this approach. It has been agreed that early preventive therapy consists of low dosis of L-DOPA, plus benserazide, L-deprenyl and dopaminergic agonists.