A common clinical manifestation of idiopathic Lewy body disease is levodopa responsive idiopathic Parkinson's disease. Infrequently features such as dementia or autonomic failure predominate. The Lewy body is also reported; as an incidental finding in 7-10% of normal individuals mostly over the age of 60 as an incidental sporadic finding in Parkinson's syndrome from other causes, mostly over the age of sixty; in an additional group of degenerative disorders at a younger age, some with familial inheritance. The incidental finding of Lewy bodies can precede clinical Parkinson's disease. It is though they do not occur as an age-related feature, although this cannot be stated with certainty. Current evidence suggests that about 10% of the population may possess the pathological substratum for idiopathic Parkinson's disease.