One of the well-recognized problems of long-term l-3,4-dihydroxyphenylalanine (l-DOPA) therapy in the treatment of Parkinson’s disease is the development of l-DOPA induced dyskinesia. These abnormal movements cause significant disability and narrow the therapeutic window of l-DOPA. Cell transplantation is one of the most promising upcoming therapies for the treatment of Parkinson’s disease, and may help alleviate or avoid l-DOPA-induced dyskinesia. However, the more recently acknowledged phenomenon of graft-induced dyskinesia is posing a major obstacle to the success of this treatment. This motor side-effect closely resembles abnormal movements induced by chronic l-DOPA treatment, yet they remain after withdrawal of the medication indicating their origins lie in the transplant. In this review, we compare these two therapy-induced adverse effects, from the way they manifest in patients to the possible mechanisms underlying their development.