Introduction: Perfectionism is an often overlooked yet consistent construct related to insomnia in the scientific literature. Perfectionism and insomnia are both highly prevalent in adolescence. However, there is a dearth of research examining mechanisms linking perfectionism with insomnia, particularly in young people. The current study aimed to investigate whether vulnerability to stress, a factor common to both constructs, accounts for the relationship between perfectionism and insomnia symptoms in a sample of adolescents. Methods: 281 Australian participants (Mage = 16.53, SD = 1.91, range = 13–19 years, 78% female) completed questionnaires assessing perfectionism, vulnerability to stress and insomnia on one occasion. Results: Vulnerability to stress accounted for the relationship between self-oriented striving perfectionism, self-oriented critical perfectionism and insomnia symptom severity in females, but not males. Females reported higher self-oriented critical perfectionism, vulnerability to stress and insomnia severity, with a stronger relationship between vulnerability to stress and insomnia symptoms observed for females. Conclusions: These results may partly explain the preponderance of insomnia in adolescent females. Possible implications for the prevention and treatment of insomnia in young people are discussed.