Intolerance of uncertainty (IU) is commonly defined as the tendency for one to interpret uncertainty as negative or threatening. Most general or non-specific measures of IU show a strong relationship with worry and generalized anxiety disorder symptoms; however, a specialized measure of intolerance of uncertainty in social situations could provide insight into the role of IU in social anxiety. The purpose of this study was the development and preliminary validation of the Intolerance of Uncertainty in Social Interactions Scale (IU-SIS), a comprehensive measure designed to assess intolerance of uncertainty in social situations. Participants consisted of a non-referred sample. Based on an exploratory factor analysis, a two-factor solution was retained, with factors labelled Social Ambiguity and Need to Reduce. Both subscales were found to have good reliability and validity. Both subscales of the IU-SIS predicted up variance on measures of social anxiety after controlling for variance explained by a well-established general/non-specific measure of IU. Overall, the IU-SIS shows promise as a tool to elucidate the association between intolerance of uncertainty and social anxiety.