Patients with asthma-like symptoms but with negative asthma tests are often misdiagnosed as having asthma and treated as asthmatics. They describe their trigger factors and symptoms very similar to those of patients with asthma. The aim of the study was to analyze differences in symptoms and trigger factors between asthma-like patients and asthmatics in order to elaborate a basis for a questionnaire for epidemiological and clinical use. A questionnaire with 54 questions about trigger factors and 137 questions about symptoms was sent to 40 patients with asthma-like symptoms and 40 with asthma, all consecutively selected from patients referred to an out-patient clinic for asthma and allergy for investigation of suspected asthma. Data were analyzed statistically in two steps using multiple logistic regression analysis. Significant differences were seen in several trigger factors and symptoms after the first analysis. After the second analysis, seven out of the 54 trigger factors and 22 out of the 137 symptoms emerged as those that most significantly discriminated between the two patient groups. These trigger factors and symptoms can be the basis of a new questionnaire with high discriminating power. Before using it, it is important to evaluate the best combination of variables, add some demographic variables and to test the reliability and validity of this new questionnaire.