['It has been shown that increased metabolic activity of primary tumour has a negative effect on survival in non-small cell lung cancer (NSCLC) staged with positron emission tomography integrated computed tomography (PET/CT). We hypothesized that an increased metabolic activity of mediastinal lymph nodes would have worse survival even if it is false.', 'Three hundred and twenty-eight consecutive patients with NSCLC histology were imaged with PET/CT within 90 days of surgery between September 2005 and March 2009. Patients who had neoadjuvant chemotherapy (n = 22), patients with prior history of NSCLC (n = 9) or other malignancies within 5 years (n = 11) were excluded from the study. Patients with negative mediastinoscopy underwent resection. Pathological results were revised according to the seventh tumor-node-metastasis staging system. Kaplan-Meier test was used for survival. Log-rank and Cox analyses were used for comparisons.', 'A total of 286 patients (262 male; mean age: 58.5 years) were evaluated. There were 22 (6.7%) operative deaths and none of the patients were lost to follow-up. The median follow-up in the remaining 264 patients was 26 months (range, 2-61 months). Tumour size, nodal spread and stage were all strongly associated with survival from NSCLC (P < 0.001). There were 63 true-positive, 65 false-positive (FP), 152 true-negative (TN) and six false-negative findings on mediastinal staging after PET/CT. The maximum standardized uptake value of primary tumour was significantly higher in FP patients than in TN patients (P = 0.012). After excluding pN2-positive patients, TN patients had better survival than FP patients (P = 0.006). Multivariate analysis showed that false-positivity of mediastinal lymph nodes was independently associated with worse survival (hazard ratio = 0.63; P = 0.02). There were 146 patients with pT1-4, pN0 treated with R0 surgical resection. Disease-free survival and overall survival were also significantly better for TN patients in completely resected group (P = 0.009 versus 0.016).'] Does false-positivity of mediastinal lymph nodes have negative effect on survival in potentially resectable non-small cell lung cancer?