Spinal instability may be a cause of juxtafacet cyst formation and the pain and disability that occur after surgical excision of the cyst. To determine the role of instability, a retrospective review of charts identified 60 facet cysts in 56 patients treated over a 6-year period. Three patients developed an asynchronous cyst at the same level but on the opposite side of the previously resected cyst and one patient had a recurrent cyst in the same location. Forty-one cysts were present in patients with radiculopathy and 16 in patients with neurogenic claudication. Two patients presented with myelopathy and one had cauda equina syndrome. Thirty-six of the 60 cysts were located at L4-5, the most mobile segment. Fifteen patients had spondylolisthesis, of whom two experienced worsening spondylolisthesis postoperatively. Seven patients had scoliosis and 20 had systemic arthritis. Fifty-five cysts were resected via mesial facetectomy. Six of the patients undergoing this procedure had transverse process fusions at initial surgery for preoperative instability. Two others required fusion for post-operative instability and increased spondylolisthesis. Follow-up review was available in 95% of patients with an average duration of 12 months. Forty patients had excellent relief of symptoms, 12 had occasional back pain, and one patient did poorly. Flexion/extension views of the spine are recommended both pre- and postoperatively to identify the need for fusion in patients with juxtafacet cysts.