Lung infections can be severe consequences of chemotherapy-induced immune defects. Aetiological causes of infection include bacteria (most commonly Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Nocardia species), viruses (eg, respiratory syncytial virus, parainfluenza virus, influenza virus A and B, and cytomegalovirus), and fungi (eg, Aspergillus, Fusarium, and Mucorales species, and Pneumocystis jirovecii). Most infections are caused by bacteria (especially Gram negative), but viruses are being increasingly identified. Diagnosis is difficult and frequently time-consuming. Treatment can be ineffective for many patients, particularly those with fungal infection. The greatest hope for the future is the availability of more targeted anticancer drugs that have fewer side-effects on the immune system.