This trial is being undertaken by the Instituto de Investigación Hospital Universitario in La Paz to determine whether the patient’s own stem cells can assist healing in complex perianal fistulae. Stem cells will be harvested from fat and will be implanted into the walls of the perianal fistula. Healing will be monitored by ultrasound up to six months after treatment. Participants will also be assessed for complications. The trial expects to recruit 10 subjects between March 2012 and December 2013.