PURPOSE: To evaluate the shape and distal end level of the lumbosacral the cal sac in normal subjects on MR imaging. MATERIALS AND METHODS: One hundred and twelve normal lumbar MRIs were reviewed. The shape and distal endlevel of the lumbosacral thecal sac on T1-weighted midine sagittal image were evaluated. The thecal sac was divided into five types, according to shape and defined as follows : type I(pointed shape) : tapering contour, with rat tail appearance ; type II(ovoid shape) : tapering smoothly, with round end ; type III(round shape) : not tapering, with round end ; type IV(pointed ovoid shape) : ending in papilae ; type V(round pointed shape) : ending in papillae. The levels of the distal end of the thecal sac were also evaluated. RESULTS: Type I was the mostcommon(43/112, 38/4%) and the second most common form was type II(31/112, 27.7%). With regard to the distal end level of the sac, 33 cases were located at the distal one third of the S2 body and 28 were at the middle one third; 16 cases were at the distal one third of the S1 body, and 14 were at the S1-S2 intervertebral disc level. All lumbosacral thecal sacs terminated between the L5-S1 intervertebral body and the distal one third of the S3 body. CONCLUSION: Lumbosacral thecal sacs ended between the L5-S1 intervertebral disc and the S3 spinal body. Most commonly, the sac terminated at the proximal one third of the S2 body. The pointed shape(type I) was most common.