ObjectivesTo describe the clinical characteristics of children with internal anal sphincter (IAS) achalasia and to evaluate the benefit of intrasphincteric injection ofClostridium botulinumtoxin.MethodsRetrospective review of the medical records of 20 patients (8 male, mean 5.8 ± 4.2 years) with severe chronic constipation and IAS achalasia. Each patient received four-quadrant, intrasphincteric injections of botulinum toxin at a dose of 15–25U per quadrant. Patients were reassessed 4 weeks-18 months after injection. We compared the clinical characteristics of these patients to 20 consecutive children (14 male, mean age 8.1 + 4.6 y) with functional constipation (control group).ResultsThe children with IAS achalasia had earlier onset of symptoms, less fecal soiling, and less withholding behavior than the control children. Response to botulinum injection was rated excellent by the parents in 60% and by the physician in 35% of children. There was wide individual variability in the frequency of defecation after therapy. Duration of response ranged from 1 week to 18 months.ConclusionsChildren with IAS achalasia have clinical characteristics differentiating them from children with functional constipation. Intra-anal injection of botulinum toxin is a safe and effective short-term treatment for these children.