We report the case of a 40-year-old woman with a submandibular sialocele (diagnosed by ultrasonography and magnetic resonance sialography) after sialoadenectomy for sialolithiasis. Type A botulinum toxin was injected percutaneously under colour Doppler ultrasonographic guidance into the sialocele and the residual salivary gland. Five months later the submandibular swelling had gone, and we gave a second injection of botulinum toxin to block any residual secretory activity. There were no side effects. This is, as far as we know, the first published report of the use of botulinum toxin to treat an iatrogenic submandibular sialocele.