Seventy patients between the ages of 18 to 30 with early spondylitis (eAS), with bilateral grade II-III sacroiliitis without syndesmophytes were examined. The control group comprised 32 patients of the same age range with lumbar disc disease (LDD) confirmed by radiculography, without changes in the sacroiliac joints. In both groups the same clinical parameters were evaluated, calculating for each the specificity, sensitivity and Youden index. Statistical analysis was done using Student's t-test and/or the chi-square test. A complex of simple clinical features was isolated suggesting presence of eAS in young subjects with persistent low back pain but without a clear-cut radiological appearance of the sacroiliac joints. The complex included: a history of morning back stiffness, swelling of knee joints, thoracic pain, clinical evidence of limited chest expansion below 5 cm, swelling of joints of lower extremities, positive Mennell's sign, and in laboratory investigations presence of raised ESR and HLA B27-antigen.