Thepurpose ofthepresent communication isto describe twopatients, onewithacongenital extradural andonewithacongenital intradural arachnoid cyst ofthespine andtoreview therelevant literature. Congenital spinal arachnoid cyst isaveryrarecause ofspinal cordcompression. Itisoneofthemost favourable spinal lesions forsurgical removal and recovery ofneurological function. Thetermcongenital isusedhereindistinction fromtheacquired variety. Acquired extradural arachnoid cysts may develop after operation whenasmall tearhasbeen madeinthespinal dura, after difficult lumbar puncture andafter spinal injury. Swansonand Fincher in1947reported fourcasesofacquired extradural arachnoid cysts after 1,700 exploratory laminectomies-an incidence of0068%.Three cases wereinthelumbar region andhadfollowed adural tearduring disc removal. Thefourth cyst wasrelated toa non-penetrating injury tothelumbarspine. Acquired intradural arachnoid cysts arealsoassociated withspinal adhesive arachnoiditis, although cystformation isnotconstantly present inthis condition. Thecongenital intradural cysts area separate entity andhavebeendescribed intheliterature under avariety ofnames-for example, spinal arachnoid diverticulae, leptomeningeal cysts, localized adhesive spinal arachnoiditis, andarachnitis adhaesa circumscripta. Theappearances ofadhesive arachnoiditis areabsent on myelography insuchcasesand, although usually single, thecysts maybemultiple. CASE 1