Patients with Parkinson's disease frequently have depression, anxiety, and obsessive-compulsive disorder. We observed two patients who had episodes of pathologic gambling. At the same time, their Parkinson's disease deteriorated and they initiated self-medication with dopaminergic drugs. In both patients, signs were present of an addiction to dopaminergic medication. Pathologic gambling ceased in these patients after a few months. The significance of an insufficient dopaminergic reward system in patients with stereotypical addictive-like behavior (e.g., pathologic gambling) is discussed in this report. The most likely explanation for this newly recognized behavioral disorder in patients with Parkinson's disease is enhanced novelty seeking as a consequence of overstimulation of mesolimbic dopamine receptors resulting from addiction to dopaminergic drugs.