An echo ultrasound technique for the measurement of the lumbar spinal canal has been assessed. Duplicate measurements of each lumbar vertebral level were made by one experienced technician on 50 healthy young males. The mean spinal canal measurement of 1.37 cm was approximately 0.2 cm less than previously reported. Seven subjects returned for reassessment. The within and between session coefficients of variation were 3.7% and 5.8%, respectively. In contrast to previous reports of three distinctly separate echoes, the authors found that the first two echoes seldom were separated clearly and most commonly formed a complex. It is concluded that if suitable interobserver and interlaboratory comparisons are made at an early stage, the reproducibility of the method is likely to be adequate for prospective epidemiologic studies.