This paper presents three cases of immunocompromised patients for whom therapeutic drug monitoring (TDM) of ganciclovir in combination with cytomegalovirus (CMV) viral load measurement was used to guide treatment. The first patient is diagnosed with Thymoma A, the second is a heart transplant recipient and the third is an HIV positive patient. These patients were all diagnosed with CMV and treated with ganciclovir. Our case studies illustrate how TDM guided dosing can be helpful in the management of these complex cases.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.