Purpose: InAustralia, radiology services are provided as full 24-hour services, 24-hour urgent out-of-hours (on-call) services, and business hoursonly service.The primary purpose of this study was to determine whether out-of-hours (11 PM'7 AM) chest x-ray (CXR) referrals are consistent with out-of-hours service expectations associated with the cost andinconvenience of calling staff in from home. A secondary objective was to determine whether the mobile chest plain film examinations are consistent with expectations of a patient's increased degree of infirmary. Method: A retrospective analysis was undertaken over 6 contiguous months for patients referred from the emergency department for CXRs out-of-hours and within standard hours (in-hours). The study population included 436 out-of-hours patients recruited into the investigation cohort and a matched cohort of 438 CXR examinations performed in-hours. The key information gleaned from the study was concordance or discordance between the clinical details relating to the actual referral and the findings of the CXR. Results: The total sample comprised 414 females (47.4%) and 460 males (52.6%). The mean age was 55.3 years, median was 56.5 years, with a range of 0'97 years. The examination type performed was 8.9% mobile compared with 91.1% departmental for the sample. It was found that there was 43.5% prevalence of abnormalities, 27.0% significant abnormalities, and 8.7% clinically significant abnormality. The predictors found for clinically significant abnormalities were increasing patient age (P<.001) and the need for mobile examination (P<.001). Performing the examination out-of-hours did not predict a clinically significant abnormality (P Â¼ .491) and similarly, gender did not predict clinically significant abnormality (P Â¼ .152). Conclusion: The results suggest that similar approaches to referrals for CXRs are applied in-hours and during the out-of-hours period which areinconsistent with the ''urgent philosophy that should accompany an out-of-hours service. Only increasing patient age and the need for a mobile CXR offered predictors of a clinical significant abnormality and this offers an insight into the potential approach to the development of referral guidelines for out-of-hours procedures.