Infections in immunosuppressed patients have always to be regarded as emergencies, as they have a high rate of complications and mortality. The most important risk factor is severity and duration of granulocytopenia. Risk scores help to identify patients who, despite their immune deficiency have a low risk of complications. Diagnostic measures to identify the causative microorganism and the source of infection is necessary. However, diagnostic investigation must not delay the immediate onset of antimicrobial treatment. Patients often have to be treated empirically as the identification of the causative microorganism or the source of infection are often unknown at the beginning of clinical symptoms. Empirical treatment has to be broad to cover possible microorganisms. Especially meningitis, abdominal infections, sepsis and pneumonia can be regarded as infectiological emergencies. Patients with these infections have to be treated with intensive antimicrobial treatment, taking into account the possible causative agents.