Preclinical evidence suggests that metformin, a widely used antidiabetic drug, may have a sensitizing effect on platinum. The purpose of this study was to evaluate the survival outcomes for non-small cell lung cancer (NSCLC) patients with type 2 diabetes mellitus (T2DM) using metformin during platinum-based chemotherapy.The clinicopathological parameters and survival data of 75 NSCLC patients with T2DM from January 2008 to December 2011 were collected and analyzed retrospectively. Patients were divided into 2 groups: metformin exposure group (n = 27) and non-metformin group (patients using other hypoglycemic agents or no drug for controlling n = 48). Univariate and multivariate analyses were performed to assess the association of metformin usage with overall survival (OS).Mean follow-up time was 58.7 months. The mean survival time was 36.74 months in the metformin group and 40.21 months in the non-metformin group. There was no significant difference in survival time between the 2 groups (P = .661). After adjusting gender, age, smoking status, tumor stage, tumor histology, and differentiation, multivariate analysis showed that metformin was not associated with the OS in NSCLC patients treated with concurrent platinum-based chemotherapy (hazard ratio: 1.071, 95% confidence interval: 0.577-1.986, P = .828).Our results indicated that metformin exposure had no significant effect on OS in NSCLC patients treated with platinum-based chemotherapy. Further studies are warranted to evaluate whether metformin could affect the survival of NSCLC patients treated with platinum-based chemotherapy.