Introduction To the best of our knowledge, there is no prediction tool for determining respiratory allergy in patients with asthma and/or rhinitis. Objectives As such, this study aimed to develop an instrument for identifying skin prick test (SPT)-negative patients with asthma and/or rhinitis. Methods This cross-sectional study screened 510 consecutive patients diagnosed with asthma and/or rhinitis between November 2009 and May 2011 in Ankara, Turkey. A structured questionnaire was the screening tool that was administered during the initial visit by the treating specialist and compared with a SPT result. All 15 variables were analysed using the logistic regression model to obtain beta values (a score) for each variable. Each variable had a score, and scores were summed up to obtain final score for each patient. Results The study included 363 patients, of which 165 (45.5%) were SPT positive. The final model included 13 variables. The lowest and highest scores were -21 and 26. A total score of 5.5 had sensitivity of 63% and specificity of 80%. The area under the receiver operating characteristic curve was 0.78. The histogram of the total scores for the study population was bimodal. Conclusions We designed a highly specific 13-item instrument for identifying SPT-negative patients. It may be used in middle income countries where allergy testing is expensive, not reimbursed or few allergy clinics are available. We think that our idea is interesting, that needs further research.