As Internet-enabled mobile device use has grown steadily, consumers increasingly appreciate the opportunity to visit commercial websites (i.e., online shops) on the go. Because mobile online shops represent under-researched consumer touchpoints with loyalty-enhancing potential, this paper seeks to answer how mobile-website design and, in particular, perceived mobile-website complexity affect individuals’ cognitive, affective, and conative responses. Powerful mobile technologies have paved the way for sophisticated mobile-website design which is associated with complexity. Given the physical constraints of mobile devices, one might assume that the previously observed positive effects of website complexity would vanish on mobile devices, replaced by confusion and dissatisfaction. The results of two empirical studies confirm this assumption, demonstrating that increasing perceived website complexity (PWC) negatively influences user satisfaction with mobile online shops. Further, increasing PWC augments individuals’ perceived confusion which, in turn, contributes to mental and behavioral disengagement. Disengagement further reduces individuals’ intention to visit the mobile online shop in the future and diminishes loyalty towards the online shop. Individuals’ negative beliefs about the performance of mobile online shopping strengthen these effects. Such negative beliefs therefore represent a manageable starting point to reduce the overall negative effects that PWC has, even indirectly, on reuse intentions.