STUDY DESIGN: A cross-sectional diagnostic study was conducted in two sessions. OBJECTIVE: To determine and compare the reliability and validity of contraindications to chiropractic treatment (infections, malignancies, inflammatory spondylitis, and spondylolysis-listhesis) detected by chiropractors, chiropractic radiologists, and medical radiologists on plain lumbosacral radiographs. SUMMARY OF BACKGROUND DATA: Plain radiography of the spine is an established part of chiropractic practice. Few studies have assessed the ability of chiropractors to read plain radiographs. METHODS: Five chiropractors, three chiropractic radiologists and five medical radiologists read a set of 300 blinded lumbosacral radiographs, 50 of which showed an abnormality (prevalence, 16.7%), in two sessions. The results were expressed in terms of reliability (percentage and kappa) and validity (sensitivity and specificity). RESULTS: The interobserver agreement in the first session showed generalized kappas of 0.44 for the chiropractors, 0.55 for the chiropractic radiologists, and 0.60 for the medical radiologists. The intraobserver agreement showed mean kappas of 0.58, 0.68, and 0.72, respectively. The difference between the chiropractic radiologists and medical radiologists was not significant. However, there was a difference between the chiropractors and the other professional groups. The mean sensitivity and specificity of the first round, respectively was 0.86 and 0.88 for the chiropractors, 0.90 and 0.84 for the chiropractic radiologists, and 0.84 and 0.92 for the medical radiologists. No differences in the sensitivities were found between the professional groups. The medical radiologists were more specific than the others. CONCLUSIONS: Small differences with little clinical relevance were found. All the professional groups could adequately detect contraindications to chiropractic treatment on radiographs. For this indication, there is no reason to restrict interpretation of radiographs to medical radiologists. Good professional relationships between the professions are recommended to facilitate interprofessional consultation in case of doubt by the chiropractors.