Labour market disengagement among youths has lasting negative economic and social consequences, yet is poorly understood. We compared four types of work-related self-perceptions, as well as vulnerability to mental health and substance abuse problems, among youths not in education, employment or training (NEET) and among their peers.Participants were from the Environmental Risk (E-Risk) longitudinal study, a nationally representative UK cohort of 2,232 twins born in 1994-1995. We measured commitment to work, job-search effort, professional/technical skills, 'soft' skills (e.g. teamwork, decision-making, communication), optimism about getting ahead, and mental health and substance use disorders at age 18. We also examined childhood mental health.At age 18, 11.6% of participants were NEET. NEET participants reported themselves as committed to work and searching for jobs with greater diligence than their non-NEET peers. However, they reported fewer 'soft' skills (B = -0.98, p < .001) and felt less optimistic about their likelihood of getting ahead in life (B = -2.41, p < .001). NEET youths also had higher rates of concurrent mental health and substance abuse problems, but these did not explain the relationship with work-related self-perceptions. Nearly 60% of NEET (vs. 35% of non-NEET) youths had already experienced ≥1 mental health problem in childhood/adolescence. Associations of NEET status with concurrent mental health problems were independent of pre-existing mental health vulnerability.Our findings indicate that while NEET is clearly an economic and mental health issue, it does not appear to be a motivation issue. Alongside skills, work-related self-perceptions and mental health problems may be targets for intervention and service provision among this high-risk population.