[A boy with involuntary movements].

A 12-year-old Dutch boy came to the paediatrician with involuntary movements of the right half of his body. He was diagnosed with Sydenham chorea as a consequence of acute rheumatic fever. Acute rheumatic fever is a rare disease in Western countries and should be recognised in time. Antibiotic prophylaxis is indicated in patients who have had acute rheumatic fever, at least until the age of 40.