This is an analysis of 19 consecutive cases of symptomatic patients with Chiari I deformities, undertaken to evaluate the long-term effect of posterior fossa decompression and duraplasty, assessed by postoperative imaging. Sixteen of the patients had syringomyelia and three had foramen magnum syndromes without a syrinx. Eighteen patients underwent posterior fossa craniectomy, subpial resection of the cerebellar tonsils, and duraplasty. Four patients were 16 years of age or younger. One of the children with syringomyelia had a posterior fossa decompression without resection of the tonsils. In the 15 patients with syringomyelia whose surgery included resection of the tonsils, the syrinx was reduced or resolved in 14. The patient whose syrinx did not change was a child with a lumbosacral lipoma. Three patients had syndromes of the foramen magnum without a syrinx, and of these only a patient with prior chemical and bacterial meningitis caused by a lumboureteral shunt failed to improve dramatically. When our patients are combined with 40 in the literature treated by decompression and duraplasty, 51 of 55 patients had reduction or resolution of the syrinx. Although it does not clearly affect the result, resection of the tonsils can be done safely.