We studied the expression in the tumour infiltrate of a T-cell activation marker, the lymphocyte-specific protein tyrosin kinase (LCK), to assess if it could be associated with a better prognostic outcome in early stage non-small cell lung cancer (NSCLC) patients. This retrospective study included 25 patients undergoing lobectomy with systematic hilo-mediastinal lymphadenectomy for pathological stage I NSCLC between July 2003 and June 2005. The presence of LCK was detected in the tumour infiltrate by immunohistochemistry on the specimens of all patients. No patient received adjuvant therapy. Twelve patients resulted LCK-positive and 13 LCK-negative. The distribution of patients according to the T-stage was similar between the LCK-positive group (1 T1a, 5 T1b, 6 T2a) and the LCK-negative group (1 T1a, 5 T1b, 7 T2a). Median overall survival (OS) time was not reached in the LCK-positive group and 30 months in the LCK-negative group (P = 0.01). OS was longer than 40 months in 75% of the LCK-positive patients and in 31% of the LCK-negative patients (P = 0.01). Median time to relapse (TTR) was significantly longer in LCK-positive patients than in LCK-negative patients (not reached vs. 25 months; P < 0.001). In conclusion, LCK-positive tumour infiltrate has been found to be associated with a significantly longer OS and TTR in patients with radically resected stage I NSCLC.