First, the current theory, minimal cognitive processing theory (MCPT) is summarized. The MCPT applies Newell and Simon’s cognitive processing theory [1] from human computer interaction (HCI) to user behavior on retail Web sites. It proposes that the two latent variables are responsible for a user staying on or leaving a Web site. Clickstream cost is the amount of cognitive processing required to reach a given page in the Web site, which is operationally defined by counting the number of Web site features and applying the Hick Hyman law. Personal cost limit is the total amount of cognitive processing that the visitor is willing to invest in the Web site. When the clickstream cost exceeds the personal cost limit, the visitor exits unless he/she has already found and purchased the desired product. From this it is deduced that the major latent variable responsible for Web site abandonment is Web site complexity (amount of cognitive processing required by the Web site). Second, an empirical study evaluating the MCPT is summarized. In this experimental study, two Web sites were created: a low-complexity Web site (with minimal features) and a high-complexity Web site (with all of the features provided as defaults by the web site building software osCommerce). The Web sites were otherwise identical. In total, 120 participants (each buying a product on both Web sites) were used. Four major hypotheses were deduced from the MCPT: the higher the Web site complexity, (a) the lower the number of products found and purchased, (b) the greater the amount of time required for purchase, (c) the greater the abandonment rate, and (d) the lower the user satisfaction. All major hypotheses were confirmed with p = .000. Secondary analyses suggest an effect of knowledge of B2C Web site design, self-reported experience in Web purchasing, and a learning effect across Web sites, as suggested by the MCPT. Third, plans for generalizing are summarized.