Second-line (SL) treatment has been shown to improve survival and quality of life outcomes for patients with stage IIIB/IV non-small cell lung cancer. However, only a minority of patients will receive SL therapy and the characteristics of this population have not been well described in the literature. In an effort to define the factors that predict who is likely to receive second line treatment, we performed an analysis on 230 patients with stage IIIB or IV non-small cell lung cancer who received first line therapy with carboplatin and paclitaxel. The median age of these patients was 63, and 144 (63%) were male, 200 (87%) had stage IV disease, 106 (46%) had a KPS of 90-100% and 124 (54%) had a KPS of 70-80%. The median number of cycles of first line chemotherapy was 4. Of these patients, 101 (44%) received second line therapy (median age 57 (range 45-76), 50% male and 37% KPS 90-100%). In the univariate analysis, younger age (P = 0.015), high baseline performance status (P = 0.002), non-squamous histology (P = 0.027), female gender (P = 0.0003), two or more cycles of therapy (P = 0.0004), four or more cycles of therapy (P = 0.001), and grade 2 or greater neuropathy (P = 0.024) were significantly associated with an increased likelihood of receiving SL therapy. In the multivariate model, high baseline performance status (OR = 2.05, P = 0.015), female gender (OR = 2.69, P = 0.001), non-squamous histology (OR = 1.98, P = 0.066), and two or more cycles of therapy (OR = 5.89, P = 0.002) remained significant. In conclusion, less than 50% of patients with stage IIIB/IV non-small cell lung cancer received SL treatment. Factors increasing the likelihood of second-line therapy include high performance status, female gender and non-squamous histology, while early termination of first-line therapy decreased the likelihood of further therapy.