OBJECTIVE To identify risk factors for bronchial asthma in a large sample of patients with rhinitis. METHODS One thousand seven hundred sixty patients with rhinitis treated at the respiratory medicine out-patient service of Hospital Universitario Virgen de Rocío in Seville (Spain) in 1997 and 1998 were studied. Six hundred forty-one (36.4%) had isolated rhinitis and 1,119 (63.6%) had rhinitis and bronchial asthma. The following variables were analyzed for both groups: 1) age, 2) sex, 3) clinical diagnosis, 4) age of onset of symptoms, 5) a family history of asthma and/or atopy, 6) housing conditions, 7) smoking, 8) a history of skin allergy, 9) recurrent episodes of respiratory infection with wheezing during early childhood, 10) a diagnosis of nasosinus polyposis, 11) atopy and sensitivity (pollens and/or household allergens), 12) peripheral blood eosinophil count. RESULTS The variables that best differentiated the group with rhinitis from the group with both rhinitis and asthma were age, family history of asthma and/or atopy, exposure to household humidity or damp, a history of skin allergy, recurrent episodes of respiratory infection with wheezing in early childhood, atopy, sensitivity to household allergens and peripheral blood eosinophil count. The probability of correctly classifying patients in the appropriate group using this model was 69.7%. Among atopic patients, the best predictive variables were the same, with the exception of household humidity/damp. The probability of correct classification using this model was 69.7%. CONCLUSIONS Patients with rhinitis have risk factors for bronchial asthma. As many such patients as possible should be identified so that long-term follow-up can take place and strategies to prevent bronchial asthma can be implemented.