OBJECTIVE This study was performed to determine if conversion from sustained release carbidopa/levodopa (SR-CL) with or without entacapone to carbidopa/levodopa/entacapone (CLE; Stalevo) improves motor functioning and quality of life in Parkinson disease (PD) patients and to assess patient tolerance and drug preference. METHODS PD patients reporting suboptimal symptom control with SR-CL were converted to CLE. The basic conversion was 1 SR-CL 25/100 to 1 25/100/200 CLE and 1 SR-CL 50/200 to 1 37.5/150/200 CLE with additional changes as necessary. RESULTS There were 62 patients with an average age of 68 years and an average disease duration of 11 years. CLE was preferred by 42 patients and SR-CL was preferred by 20 patients. In those that preferred CLE, Unified Parkinson Disease Rating Scale (UPDRS) mentation and motor subscores, Parkinson Disease Questionnaire-39 (PDQ-39) quality-of-life activities of daily living (ADL) and bodily discomfort subscores, and Epworth Sleepiness Scale (ESS) scores were significantly improved. There were no significant changes in any measures in the group that preferred SR-CL. Common adverse effects in the group that preferred CLE included nausea, vomiting, increased dyskinesia or off time, dizziness, and somnolence. The most common adverse events in the group preferring SR-CL were increased off time or dyskinesia, nausea, and vomiting. CONCLUSIONS A majority of patients suboptimally controlled on SR-CL can be successfully converted to CLE with improvements in motor function, quality of life, and sleepiness. Older patients, with longer disease duration not previously exposed to entacapone, may better tolerate CLE after the addition of entacapone.