Myoclonus is common in neurodegenerative disorders and may be in small or large amplitude. In dementia with Lewy bodies, it occurs as moderately sized jerks in about 1/3 of cases. The combination of dementia, early parkinsonism, hallucinations, cognitive fluctuations, and myoclonus is strongly suggestive of the dementia with Lewy body diagnosis. The major differential diagnosis is Alzheimer’s disease, although other diagnoses should be considered. The physiology of the myoclonus is cortical. Treatment should be tailored to the patient’s circumstances. Drugs used for cortical myoclonus are the most useful. Monitoring is necessary for therapeutic response and possible limiting side effects.