How safe is the surgery to fix a chiari malformation?

Moderately risky: Chiari decompression surgery is considered moderate risk surgery. In other words, its not like having your appendix or hernia repaired but its also not like having a complex brain tumor or aneurysm worked on either. The major risks of this surgery are severe (sometime chronic) neck pain, bleeding, infection, and a small risk of spinal fluid leak. The more scary risks (stroke) are very rare.

Usually very safe: The procedure, when done in the hands of an experienced neurosurgeon, is very safe. There are always the risks of bleeding and infection, but these are usually easily manageable. Talk to your surgeon about the specific risks.