Ganglion cyst: how often do they grow back?

Rarely: About 15% of the time a ganglion cyst can be recurrent. A lot depends on the incidence of infection and other factors (ie, drugs) that can influence primary healing.

< 5% with surgery: Ganglion cysts are managed by being left alone or hit with a heavy book like a bible - high recurremce rate. If treated by aspiration and steroid injection - i tell my patients two thirds will come back. Lastly if treated by surgical excision - the recurrence rate should be less than 5%.