The lumbar spine was examined radiologically for the presence of spondylolysis and spondylolisthesis in 936 asymptomatic soldiers prior to military placement and in 662 soldiers complaining of low back pain. The overall incidence of spondylolysis was 9.7% in both groups, but bilateral spondylolysis was more prone to be associated with symptoms than a unilateral defect. In the symptomatic group the incidence of spondylolisthesis was 5.3% but only 2.2% in the asymptomatic group. The defect was seen in the oblique views only in 18.7% of the cases of spondylolysis. The precise diagnosis is important for vocational counselling and military placement.