Research on the link between affinity for solitude (a tendency to enjoy time alone) and psychosocial adjustment among adolescents has been mixed; however, this may depend on whether time spent alone is motivated by positive (self-reflection, creative pursuits) or reactive (negative affect, avoiding social interaction) factors. The current study investigated affinity for solitude and motivations for spending time alone among 1072 early to mid-adolescents (Mage = 12.48 years, age range = 10–16, 49.8% female). Higher reactive solitude predicted depressive symptoms, peer victimization, and lower self-esteem, controlling for previous scores on these adjustment indicators. For social anxiety and friendship quality, there were significant 3-way interactions between affinity for solitude, reactive solitude, and frequency of time spent alone, indicating that the relation between affinity for solitude and these latter adjustment indicators depends on why and how often youth spend time alone. Findings indicate that attention should be given to youth who spend time alone for reactive reasons, as this appears to be associated with negative adjustment.