Toxicity and efficacy of pemetrexed monotherapy in advanced non-small-cell lung cancer patients with impaired renal function treated between May 2009 and May 2012 at Gifu University Hospital were retrospectively analyzed. A total of 10 and 17 patients had a creatinine clearance rate (Ccr) of <45 mL/min and ≥45 mL/min, respectively. The median age was higher in the Ccr<45 mL/min group (78.9 years) than in the ≥45 mL/min group (65.2 years). The rate of neutropenia above Grade 3 was 30% in the Ccr<45 mL/min group and 6% in the ≥45 mL/min group. Therefore, reducing the dose of pemetrexed should be considered in patients with impaired renal function. Non-hematologic toxicities were not correlated with the renal function. There was no treatment-related death, and most of the toxicities were mild and tolerable. Stable disease was observed in 6 patients (60%) in the Ccr<45 mL/min group, and in 12 patients (70%) in the Ccr≥45 mL/min group, although some patients in both groups showed neither complete nor partial responses. The disease control rate and median progression-free survival time were 60% and 2.8 months in the Ccr<45 mL/min group, and 70% and 2.9 months in the Ccr≥45 mL/min group, respectively. Thus, in this analysis, treatment with pemetrexed resulted in clinically equivalent efficacy in advanced non-small-cell lung cancer patients regardless of the state of renal function.