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Importance: Little is known about the long-term economic and social outcomes for children with longitudinally assessed comorbid externalizing and internalizing symptoms, especially compared with children with externalizing symptoms or internalizing symptoms only.

Objective: To examine the association between childhood trajectories of externalizing, internalizing, and comorbid symptoms and long-term economic and social outcomes.

Design, setting, and participants: A 32-year prospective cohort study linked with administrative data was conducted in school-aged participants aged 6 to 12 years in the Québec Longitudinal Study of Kindergarten Children (N = 3017) followed up from 1985 to 2017. Data analysis was conducted between August 1, 2021, and March 31, 2022.

Exposures: Teacher-rated behavioral symptoms were used to categorize children from age 6 to 12 years into developmental profiles using group-based trajectory modeling.

Main outcomes and measures: Multivariable regression models were used to test the association between childhood symptom profile group and adult employment earnings, welfare receipt, intimate partnership status, and having children living in the household. Participant sex, IQ, and socioeconomic background were adjusted for.

Results: Of 3017 participants in this sample, 1594 (52.8%) were male and 1423 (47.2%) were female. Per confidentiality rules established by Statistics Canada, income variables were rounded to base 100 and count variables were rounded to base 10; the mean (SD) age was 37 (0.29) years at follow-up. Four symptom profiles were identified: no/low (n = 1369 [45.4%]), high externalizing (882 [29.2%]), high internalizing (354 [11.7%]), and comorbid (412 [13.7%]) symptoms. Compared with the no/low symptom profile, participants in the high externalizing-only profile earned $5904 (95% CI, -$7988 to -$3821) less per year and had 2.0 (95% CI, 1.58-2.53) times higher incidence of welfare receipt, while participants in the high internalizing group earned $8473 (95% CI, -$11 228 to -$5717) less per year, had a 2.07 (95% CI, 1.51-2.83) higher incidence of welfare receipt, and had a lower incidence of intimate partnership (incident rate ratio [IRR], 0.89; 95% CI, 0.80-0.99). Participants in the comorbid profile fared especially poorly: they earned $15 031 (95% CI, -$18 030 to -$12 031) less per year, had a 3.79 (95% CI, 2.75-5.23) times higher incidence of annual welfare receipt, and were less likely to have an intimate partner (IRR, 0.71; 95% CI, 0.63-0.79) and children living in the household (IRR, 0.86; 95% CI, 0.80-0.92). Estimated lost earnings over a 40-year working career were $140 515 for the high externalizing, $201 657 for the high internalizing, and $357 737 for the comorbid profiles.

Conclusions and relevance: In this cohort study, children exhibiting sustained childhood high externalizing, high internalizing, or comorbid symptoms were at increased risk of poor economic and social outcomes into middle age. These findings suggest that children exhibiting comorbid problems were especially vulnerable and that early detection and support are indicated.