OBJECTIVE: In health services research, obtaining objective measures of pulmonary function to classify asthma severity is often not possible. Researchers must rely on methods such as frequency of self-reported symptoms and patient perceived severity. This study examined the relationship between FEV1 determined severity and severity determined by patient-reported information. METHODS: Data from adult patients with asthma were obtained from a pulmonary clinic via chart review and patient self-report during a scheduled physician visit. Patients in acute exacerbation were excluded. Patient-Perceived Severity (PPS) was determined by asking "How severe do you think your asthma is?" with a five-point Likert scale from Very Mild to Very Severe. Overall Symptom-derived Severity (OSS) and Nocturnal Symptom-derived Severity (NSS) were determined from two separate questions regarding symptom frequency during the preceding four weeks. Responses were based on the NHLBI 1997 Asthma Guidelines. Pulmonary function tests were obtained the same day as part of standard care. FEV1-Determined Severity (FEV1-DS) was derived by comparing the FEV1 with the Guideline classification of severity based on spirometry. Three severity categories were derived for each severity method. Percent agreement between FEV1-DS and each patient-reported severity was determined by constructing 3x3 tables. Correlations (Spearman's rho) were conducted between FEV1-DS and the patient-reported severity measures. RESULTS: 57 patients with a mean FEV1 percent predicted of 80.2%(27.5) were studied. The percent agreement between FEV1-DS and PPS was 59.7% (33.3% over-estimate, 7.0% under-estimate); 56.4% between FEV1-DS and OSS (14.5% over-estimate, 29.1% under-estimate); and 40.7% between FEV1-DS and NSS (25.9% over-estimate, 33.3% under-estimate). The correlations between FEV1-DS and PPS were 0.58 (p<0.01); 0.53 with OSS (p<0.01); and 0.13 with NSS (p=0.13). CONCLUSIONS: PPS and OSS demonstrated reasonable agreement and correlation to FEV1-DS, albeit opposite trends in over- and under-estimates. These two measures of asthma severity appear useful for population based studies when FEV1 is unavailable.