- When evaluating patients with respiratory tract infections (RTI), physicians have to judge and decide whether the patient has pneumonia or not. This decision is usually made by clinical assessment alone and/or by performing a chest X-ray. The aim of this study was to determine the reliability of physicians' judgements relating to the presence of pneumonia in RTI patients by clinical assessment alone compared with chest X-ray. A prospective, clinical study. Primary care clinics and a university hospital in southern Israel. Two-hundred-and-fifty ambulatory patients with febrile RTI were included in a prospective study. On the basis of a medical interview and physical examination alone physicians were asked to make judgements relating to the study question, and these judgements were compared with the results of chest X-rays. Physicians' judgements of pneumonia had a sensitivity of 74% (49-90%), a specificity of 84% (78-88%), a negative predictive value of 97% (94-99%) and a positive predictive value of only 27% (16-42%), compared to the results of chest X-ray. We conclude that the ability of physicians to negate X-ray confirmed pneumonia by clinical assessment in febrile adult RTI patients is good, but that their ability to successfully predict this condition is poor.