Background: Synovial arteriovenous malformation is rare.
Case characteristics: We present three children with recurrent monoarthritis secondary to synovial arteriovenous malformation.
Outcome: Two children underwent excision of arteriovenous malformation. Another child had diffuse arteriovenous malformation, which was inoperable.
Message: Synovial arteriovenous malformations should be considered in the differential diagnosis of monoarthritis, especially of the knee.