Purpose The TNM staging remains the best prognostic descriptor of lung cancer; however, new independent prognostic factors are needed, particularly for early stage disease. Methods An evaluation of the pleural lavage cytology (PLC) was performed in 436 consecutive NSCLC patients who underwent surgical resection; clinical, pathological and follow-up data were available for 414 patients. Results The PLC was positive in 15 patients (3.6 %). The overall five-year survival was 35.9 % in PLC-positive and 57.8 % in PLC-negative patients ( p  = 0.004). To compare groups with the same prognostic characteristics, the analysis was restricted to p-stage I patients, but the survival remained worse in the PLC-positive patients (42.9 vs 69.4 %; p  = 0.001). Recurrence was also observed more frequently in PLC-positive cases: 69.2 vs 34.5 %, OR 4.28 (95 % CI 1.29–14.18; p  = 0.01). Among the PLC-positive patients, no difference between the local (44.4 %) and distant (55.6 %) relapse patterns was found ( p  = 0.82). The multivariate analysis identified four independent prognostic factors: age ( p  < 0.001), disease stage ( p  < 0.001), gender ( p  = 0.025) and PLC status ( p  = 0.012). Conclusions PLC is an independent prognostic factor for NSCLC. PLC-positive NSCLC patients have a worse overall survival and a higher recurrence rate, even in stage I disease. PLC-positive patients should be considered a high risk category, who should potentially be eligible for adjuvant therapy regardless of their p-stage.