The neurological disease causes uncontrolled shaking, stiffness and slow movement.
In the experimental treatment, genes are injected directly into the brain. A report in The Lancet Neurology journal explains how researchers used a virus to add genes to brain cells.
About half the patients who got the gene therapy showed improvement in their symptoms.
Researchers say gene therapy has become reality for Parkinson's disease and could open the door to treat other neurological problems such as Alzheimer's.