Objectives: Mediastinal lymph node staging of NSCLC by initial endosonography and confirmatory mediastinoscopy is recommended by the European guideline. We assessed guideline adherence on mediastinal staging, whether staging procedures were performed systematically and unforeseen N2 rates following staging by endosonography with or without confirmatory mediastinoscopy. Material and Methods: We performed a multicentre (n = 6) retrospective analysis of NSCLC patients without distant metastases, who were surgical candidates and had an indication for mediastinal staging in the year 2015. All patients who underwent EBUS, EUS and/or mediastinoscopy were included. Surgical lymph node dissection was the reference standard. Guideline adherence was based on the 2014 ESTS guideline. Results: 330 consecutive patients (mean age 69 years; 61% male) were included. The overall prevalence of N2/N3 disease was 42%. Initial mediastinal staging by endosonography was done in 84% (277/330; range among centres 71-100%; p <.01). Confirmatory mediastinoscopy was performed in 40% of patients with tumour negative endosonography (61/154; range among centres 10%-73%; p <.01). Endosonography procedures were performed ‘systematically’ in 21% of patients (57/277) with significant variability among centres (range 0-56%; p <.01). Unforeseen N2 rates after lobe-specific lymph node dissection were 8.6% (3/35; 95%-CI 3.0-22.4) after negative endosonography versus 7.5% (3/40; 95% CI 2.6-19.9) after negative endosonography and confirmatory mediastinoscopy. Conclusion: Although adherence to the European NSCLC mediastinal staging guideline on initial use of endosonography was good, 30% of endosonography procedures were performed insufficiently. Confirmatory mediastinoscopy following negative endosonography was frequently omitted. Significant variability was found among participating centres regarding staging strategy and systematic performance of procedures. However, unforeseen N2 rates after mediastinal staging by endosonography with and without confirmatory mediastinoscopy were comparable.