Small cell undifferentiated carcinoma (SmCC) of the gastrointestinal tract (GIT) is a rare and highly aggressive malignancy. To date, fewer than 1,000 cases have been reported, with an estimated prevalence of 0.1% to 1% of all gastrointestinal (GI) tumors. Data on the disease are scarce due to its rarity and the fact that most authors have focused on one site within the GIT. In light of the limited data and its perceived similarity to SmCC of the lung, the disease has usually been treated as the latter. Nevertheless, recent clinicopathologic and molecular data imply several differences between the two entities, questioning the extent to which extrapolations from one to the other can be made. We review the available data on GI SmCC with emphasis on outlining its clinicopathologic features and the recommended treatment approach.