Oscillometry is becoming increasingly widespread because it allows lung function tests to be performed independently of patient cooperation. This procedure could enormously improve diagnostic decision making in primary care. However, the diagnostic accuracy with which asthma, COPD and, more generally, airway obstruction can be predicted remains unclear up to now.The aim was to determine the diagnostic accuracy of oscillometry for the detection of airway obstruction, and for the differential diagnosis of asthma and COPD.Cross sectional diagnostic study. We consecutively recruited patients who came to a large pulmonologist's practice in ambulatory care in Munich for a routine examination. Index test: First, oscillometry was performed (key biomarkers: R5, R5-20, AX). Reference standard: After that, routine investigation with whole body plethysmography was performed. An obstructive airway disease was diagnosed when Forced Expiratory Volume in the first second / Vital Capacity (FEV1/ VC) was < 0.70. Two by two tables will be calculated to determine sensitivity, specificity, positive and negative predictive values for the detection of airway obstruction. Subgroup analyses are performed to determine the diagnostic accuracy for asthma and COPD.The recruitment process has been successfully completed. From early August to late October 2025, a total of 500 patients were recruited.The data is currently being entered and analysed. The final results will be presented at the conference.The results of this large-scale diagnostic study in ambulatory care can help to better assess the diagnostic usefulness of oscillometry for primary care.