The growing popularity of Group Decision Support Systems (GDSS) has been supported by, and has given rise to, a burgeoning academic literature on GDSS since the mid-1980s. Although there is a growing body of laboratory experiment findings, the results are inconclusive. Field studies in real organization settings show all the more different results form the experimental studies. This paper systematically reviews the existing case, field, and laboratory decision room type GDSS studies. It, then, explores the plausible reasons for the inconsistent findings across the laboratory studies, and especially between field and laboratory research. It suggests five main factors for the inconsistent findings in previous GDSS research: contextual pressures, tasks, group characteristics, technical configurations, and comparability of measures.