The complexity of managing critically ill patients has increased since the early establishment of intensive care units in the 1950s. Despite of the fact that the number of drugs available to clinicians has increased, the understanding of the pharmacokinetics of individual drugs in specific disease states is still a matter of concern. Among the pharmacokinetic processes which may be affected in this patient population, drug distribution is a very important one. Changes in drug distribution may cause inadequate drug exposure at the infection site and consequently influence clinical outcome. Since drug distribution is dependent on a plethora of factors, including the physicochemical characteristics of the drug, we will focus on the most common mechanisms responsible for altered tissue distribution. These include changes in protein binding, fluid shifts, and pH changes. Although less common, alterations in organ perfusion may also play a role, particularly in heart failure patients. Despite great advances in understanding the distribution of antibacterial drugs, further studies are needed to define the consequences of changed drug distribution in critically ill patients on dosing regimens and clinical outcome.