Background: Few case reports describe an increase in the size of syringomyelia and the worsening of neurologic symptoms after surgery for foramen magnum decompression. We report three such cases. Material and method: Retrospective review of patients with Chiari malformation (CM) and syringomyelia operated at the Erzurum Regional Hospital, Department of Neurosurgery between 1 January 2008 and 18 June 2018. Results: A total of 118 patients were operated during the study period. Of the 118 patients, 81 were females, 37 were males. Ages range between 4 and 82 years, mean 38 years. Cervical or thoracic syringomyelia was found in 81 patients. Decompressive surgery with duraplasty was performed in all patients, and the patients were followed at least 2 years. The syrinx was the same or smaller in volume in 74 patients postoperatively, however, in three patients (3.7% of all patients with syringomyelia), the syrinx increased in volume. Conclusions: In this study, it was observed that an improvement or resolution of syringomyelia in 74 patients (91.3%) after decompression. There were no changes in the cavity in 4 and increased size in 3.