OBJECTIVES: The main objective of present study was to evaluate the discriminatory ability of the HRQOL in relationship to severity degree in asthma patients. METHODS: Cross-sectional descriptive study carried out in a semirural county of 110.000 inhabitants. Patients were included in stable asthma phase, and classified into three groups: mild, moderate, and severe. Assessment included spirometry, sociodemographic, clinical data (morbidity and use of health-services), and two HRQOL questionnaires: one generic, the Nottingham Health Profile (NHP), and one specific, the St. George's Respiratory Questionnaire (SGRQ). HRQOL scores were standardized by age and gender according to Spanish population norms. RESULTS: Out of 385 patients with asthma, 52 were excluded because different reasons, and 333 adult patients were included with a mean age of 42 years (64% were females). Patients were classified according to asthma severity degree: mild, 140 patients (42%), moderate, 116 patients (35%), and severe, 77 patients (23%). Median time of evolution of asthma was 8 years, and most of patients (80.1%) had less than 3 asthma attack per year. NHP mean (SD) standardized score was 0.20 (1.21) for mild patients, 0.68 (1.43) moderate, and 1.21 (1.57) severe. SGRQ mean standardized score (SD) was 2.75 (2.11) for mild patients, 3.61 (2.31) moderate, and 4.17 (2.44) severe. Although patients with mild asthma had low impaired FEV1, and NHP scores close to that of general population, they showed substantial effects on HRQOL using the specific instrument, the SGRQ. CONCLUSIONS: Both HRQOL instruments are associated to asthma severity degree but discriminatory ability was higher for the disease-specific instrument. In addition, SGRQ seems to be more useful than NHP and traditional clinical measures identifying the mild severity degree impact.