Insulin-like growth factor-I (IGF-I) is a mitogenic and anti-apoptotic factor. Serum IGF-I concentration is related to some cancer risk and tumor progression. The aim of this research was to study the association of preoperative serum IGF-I concentration with clinicopathological parameters and prognosis of non-small cell lung cancer (NSCLC). Preoperative serum IGF-I concentration was measured in 80 consecutive patients with NSCLC who underwent radical lung cancer resection, and 45 patients with benign pulmonary lesion (BPL) by using enzyme linked immunosorbent assay (ELISA). The results showed that the serum IGF-I concentration was elevated and correlated with clinicopathological parameters and overall survival (OS) in NSCLC patients. Serum IGF-I concentration was significantly higher in patients with NSCLC than in those with BPL. The IGF-I concentrations were significantly higher in NSCLC patients with a parts per thousand yenT2, N1-3, and in IIIA-IV but not in those with < T2, N0, or IA-IIB. The increased serum IGF-I concentration was significantly correlated with poor prognosis. Our data show the positive correlation between IGF-I serum concentration and the tumor size for the first time. It seems that IGF-I related to the progression of lung cancer may depend on autocrine/paracrine function. In addition, our study reveals that higher serum IGF-I concentration is correlated with larger tumor size, advanced stages, local lymph node metastasis and worse prognosis, indicating that endocrine IGF-I is also important for the progression for NSCLC.