['Chronic obstructive defecation can occur in patients with Hirschsprung Disease (HD) and internal anal sphincter (IAS) achalasia. Injection of Botulinum Toxin (BoTox) into the IAS can temporarily relieve obstructive defecation, but can be challenging when performed by tactile sense alone. We compared results of BoTox injections with and without ultrasound (US) guidance.', "We retrospectively reviewed BoTox injections into the IAS for obstructive defecation over 5years. Analyzed outcomes included short-term improvement, defined as resolution of enterocolitis, new ability to spontaneously defecate, and/or normalization of bowel movement frequency 2weeks post-operatively, as well as requirement of more definitive surgical therapy (myotomy/myomectomy, colectomy, colostomy, cecostomy/appendicostomy, and/or sacral nerve stimulator implantation). Outcomes were compared using t-test and Fisher's Exact test, with significance defined as p<0.05.", 'Twelve patients who underwent BoTox injection were included, including 5 patients who underwent injections both with and without ultrasound. Ten underwent an ultrasound-guided injection (13 injection procedures), 5 of whom had HD. Seven underwent an injection without ultrasound guidance (17 injection procedures), 5 of whom had HD. Procedures performed with US resulted in greater short-term improvement (76% versus 65% without ultrasound) and less requirement of a definitive procedure for obstructive defecation (p<0.05).'] Does ultrasound-guided intrasphincteric botulinum toxin injection relieve obstructive defecation due to Hirschsprung 's disease and internal anal sphincter achalasia?