Familial syringomyelia outside of trauma, tumor, or infection has been reported. Cases are presented that highlight the possible connection between familial syringomyelia and the Chiari 0 malformation. We report on 11-year-old twin brothers both with syringomyelia. Magnetic resonance imaging further revealed that one brother had Chiari I malformation and the other had Chiari 0 malformation. Both underwent posterior fossa decompression with radiologic improvement of their syringes. These case reports lend credence to earlier reports of improvement in syringomyelia following posterior fossa decompression in the absence of Chiari I malformation, the so-called Chiari 0 malformation. In addition, these case reports should influence the manner in which familial syringomyelia without tonsillar ectopia is defined and addressed, that is, posterior fossa decompression versus shunting of the syrinx, thereby addressing the potential cause of the syringomyelia and not only the enlarged cavity itself.