With the increased number of international travelers and that of immunosuppressive therapies, it is usual to see immunosuppressed patients asking for advice before a trip exposing them to a certain risk of infectious diseases. The difficulty with vaccinating the immunosuppressed is twofold as risk as well as effectiveness has to be taken into account. Immune responses to vaccines are more effective if they are based on immunological memory. In other cases, antibody level determination may be useful to assess the potential for protection. Clinical cases are presented to illustrate difficulties faced by the general practitioner.