People possess an innate need to belong that drives social interactions. Aberrations in the need to belong, such as social anhedonia and social anxiety, provide a point of entry for examining this need. The current study used experience-sampling methodology to explore deviations in the need to belong in the daily lives of 245 undergraduates. Eight times daily for a week, personal digital assistants signaled subjects to complete questionnaires regarding affect, thoughts, and behaviors. As predicted, higher levels of social anhedonia were associated with increased time alone, greater preference for solitude, and lower positive affect. Higher social anxiety, in contrast, was associated with higher negative affect and was not associated with increased time alone. Furthermore, greater social anxiety was associated with greater self-consciousness and preference to be alone while interacting with unfamiliar people. Thus, deviations in the need to belong affect social functioning differently depending on whether this need is absent or thwarted.