Background: Intraspinal facet cyst or juxta-facet cyst is a term that includes synovial and ganglion cysts in the spine. Facetal synovial cysts are fluid-containing synovial outpouchings arising from degenerated facet joints resulting from chronic hypermobility of the joints. These cysts can cause low back pain, radicular leg pain, and in rare cases cauda equina syndrome. Case description: In this report, we would like to present the occurrence of incomplete cauda equine syndrome resulting from a facet synovial cyst in a 65-year-old woman who presented with weakness in both lower limbs, difficulty in walking, and saddle anesthesia. The symptoms resolved following a posterior decompression, cyst excision, and instrumented fusion surgery. Conclusion: This report highlights the occurrence of acute cauda equina syndrome in a 65-year-old woman resulting from an L4–L5 facet synovial cyst. Prompt diagnosis and immediate surgical intervention in the form of decompression and fusion surgery lead to a favorable outcome. Clinical message: Acute cauda equina syndrome in a patient with a lumbar facet cyst is a relatively uncommon presentation. It requires early diagnosis and immediate surgical intervention in the form of decompression to prevent neurological deterioration and to have a favorable outcome.