['To determine the frequency of pulmonary embolism (PE) diagnosis when different alternative diagnoses were considered most likely before testing, because the relationship between specific alternative diagnoses and the diagnosis of PE has not been explored.', "This study was a preplanned secondary analysis of a prospective study of the diagnosis of pulmonary embolism conducted in the emergency department (ED) of an urban university hospital. Physicians were queried as to their most likely pretest diagnosis when they ordered any of the following tests to evaluate possible PE: D-dimer, contrast-enhanced computed tomography of the chest, ventilation-perfusion lung scan, or pulmonary angiogram. To compare the frequency of PE diagnosis across alternative diagnoses, risk ratios, 95% confidence intervals (CI), and p-values using Fisher's exact test were calculated.", 'Six hundred seven patients were enrolled, and 61 had PE. Physicians thought PE was the most likely pretest diagnosis in 162 (26.7%) patients, and 20.4% (95% CI = 14.4% to 27.4%) of these patients had PE. For four alternative diagnoses, PE was diagnosed less frequently than when PE was considered most likely: musculoskeletal pain (2.2%, 95% CI = 0.4% to 6.2%), anxiety (1.7%, 95% CI = 0.0 to 9.2%), asthma or chronic obstructive pulmonary disease (0, 95% CI = 0.0 to 10.9%), and viral syndrome (0, 95% CI = 0.0 to 14.3%).'] Is the probability of pulmonary embolism a function of the diagnoses considered most likely before testing?