The present study was carried out on 200 subjects with 100 asymptomatic control and100 symptomatic cases of low backache , sciatica and neurogenic claudication of more than 6 months duration of age group 30 -80 years. The aim of the study was to find out the dimensionsof the lumbar spinal canal on plain radiographs of the lumbar spine in normal and symptomatic subjects and to compare them. It was found that the lower normal limit of the transverse diameter of the lumbar spinalcanal was 20 mm and antero-posterior diameter was 15.2 mm on plain radiographs ofasymptomatic healthy subjects. Anteroposterior diameter was found to be more adversely affected in narrow spinal canal