The rapid evolution of information and mobile technologies enables consumers to use media content whenever and wherever they want. These developments have resulted in a new form of target audience behavior called “media multitasking.” Media multitasking describes simultaneous exposure to two or more types of media content. Extant research on this subject concentrates on the influence of media multitasking on message comprehension and recall for editorial content (i.e., TV programs). To date, limited research has examined whether simultaneous exposure to two advertisements on two devices benefits or harms message effectiveness. The current research attempts to fill this research gap by investigating the effect of media multitasking with TV and mobile Internet advertisements on message effectiveness. In particular, an online experiment confirms the assumption that media multitasking harms message effectiveness. Contrary to the theoretically derived hypotheses, it does not matter whether consumers are exposed to the same or different advertising messages during media multitasking situations. The consideration of two moderating variables—gender and media multitasking frequency—offers further insights into the individual factors that affect message effectiveness during simultaneous versus sequential media exposure.