To show the frequent association of synovial cysts and facet effusion. MR studies of 26 patients with lumbar synovial cysts were reviewed for sex/age incidence, anatomic location, multiplicity of cysts and associated pathologies. All studies were reviewed for presence of facet effusion. 26 patients had 39 MRI documented synovial (17 females, 9 males). Age distribution: 41 – 79 years. Location of cysts: L4/5 = 29, L3/4 = 6, L5/S1 = 3, L1/2= −;1. 36 synovial cysts showed facet effusion. 19 patients also had facet effusions at adjoining motion segments or at contralateral joints. Synovial cysts were found in anterior (n=20), posterior (n=13), anterior-posterior (n=3) positions. 18 patients had cysts localized to one single facet joint, 8 patients showed synovial cysts at multiple facet joints. The frequent coexistence of synovial cysts and facet effusion in our material suggests a causal relationship. External herniation of synovium from a fluid expanded joint space appears to be the most plausible pathologic mechanism.