Data regarding treatment outcomes and prognosis in pneumonia that occurs after lung cancer chemotherapy are lacking. We performed a retrospective study of 84 patients with clinically suspected bacterial pneumonia after cytotoxic chemotherapy for lung cancer. Small cell carcinoma was the most common histological type (36.9%, n = 31), followed by squamous cell carcinoma (35.7%, n = 30) and adenocarcinoma (21.4%, n = 18). The most frequent pathogen was Streptococcus pneumoniae (n = 14), followed by Klebsiella pneumoniae (n = 10), Staphylococcus aureus (n = 8), and Pseudomonas aeruginosa (n = 7). Of 84 patients, treatment outcome was determined for 80; the outcome was success in 52 (61.9%) and failure in 28 (33.3%); outcome remained undetermined for 4 patients (4.8%). Based on multivariate analysis, tachypnoea (respiratory rate ≥20/min) was the only significant predictor of treatment failure (odds ratio 4.79, 95% confidence interval 1.17-19.70; p = 0.030). In conclusion, bacterial pneumonia after cytotoxic chemotherapy for lung cancer was found to be caused more often by S. pneumoniae and K. pneumoniae than P. aeruginosa, and treatment failure leading to death was found to be high. Tachypnoea was independently associated with treatment failure in this population.