This study aimed to investigate the ways subtypes of social withdrawal and dimensions of solitude are related to existential concerns in emerging adulthood. The links between social withdrawal/solitude and existential well-being are a highly neglected research issue. Participants were 774 emerging adults (50.4% males) aged 18–25 ( M = 20.07) from Greece. They completed measures on social withdrawal, solitude, authenticity, meaning in life, existential anxiety, and existential loneliness. We used structural equation modeling to analyze the data. Results indicated that shyness, avoidance, and isolation were associated with more existential concerns, whereas unsociability was associated with less existential concerns. The solitude dimensions—enlightenment, freedom, intimacy, and loneliness—were differentially associated with existential concerns, with enlightenment exhibiting the most existential benefits. Findings showed that existential well-being is dependent on emerging adults’ quality of withdrawal experiences and ability to make constructive use of solitude.