Observer variation in interpreting radiograph of the spine in 70-year-old Danish women has been examined. The women joined a general health investigation as part of an epidemiologic screening for osteoporosis. Two experienced radiologists examined independently 280 sets of lateral radiographs of the spine to disclose fractures. The radiographs were examined four times, each examined at two different occasions by each radiologist. Overall intra-observer agreement was 88% and 87% when asked for presence or absence of fractures, irrespective of fracture localization. When accidental occurrence of agreement was taken into account (kappa analysis) intra-observer variation was reduced to 64% and 62%. The overall inter-observer agreement was 75%, but reduced to 47% when accidental occurrence of agreement was noted. Kappa analysis in testing observer variation indicates that a considerable part of agreement can be ascribed to chance alone. This seriously questions the hitherto used definition of osteoporosis.