Significant changes in the epidemiology of infectious complications in cancer patients have emerged during the past decade. Among blood culture isolates from febrile neutropenic patients, Gram-positive pathogens have become predominant, and an increasing spread of methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci must be taken into consideration. Risk factors such as indwelling venous catheters or chemotherapy-induced mucosal damage are associated with an increased incidence of Gram-positive infections. Invasive fungal infections, particularly invasive aspergillosis, have become most important in severely neutropenic patients and are associated with fatality rates of 40-60%. The use of nucleoside analogues and the CD52-antibody alemtuzumab induce a long-lasting lymphopenia facilitating the occurrence of opportunistic infections specifically caused by viruses and fungi. In elderly patients undergoing intensive myelosuppressive chemotherapy, infectious complications may be managed as successfully as in younger patients by appropriate antimicrobial therapy. The broad use of fluoroquinolones for antibacterial prophylaxis in neutropenic patients may lead to very high resistance rates among Gram-negative bacilli such as E. coli. In patients given moxifloxacin for infection prevention, unacceptably large numbers of Clostridium difficile-associated enterocolitis have been reported.