Socioeconomic disadvantage in childhood is common among youth not in education, employment or training (NEETs). However, the evidence on other adverse childhood experiences as determinants of NEET remains scarce. We use Finnish longitudinal register data on a 20% random sample of households with 0-14-year-old children in 2000 to assess the childhood determinants of NEET. For an analytical sample of 99,137 children born 1986-1993, family socioeconomic resources, parental psychiatric disorders and substance abuse, parental death, living in a single-parent household and out-of-home placement under age 13 were used to predict NEET at the age of 18. We show that family socioeconomic disadvantage is strongly associated with NEET (e.g. odds ratio for parental basic education 5.33, 95% confidence interval 4.77, 5.95), whereas associations between adverse childhood experiences and NEET are more moderate (e.g. odds ratio for parent hospitalised for psychiatric disorder 1.86, 95% confidence interval 1.63, 2.12) and largely explained by socioeconomic factors. These associations were mostly similar by gender. The results suggest that parental socioeconomic resources are more important than adverse childhood experiences for the educational and employment transitions of young adults. Thus, supportive social policy for socioeconomically disadvantaged families may smooth these transitions.