Importance: Policy changes since early 2017 have resulted in a substantial expansion of Latino or Latina immigrants prioritized for deportation and detention. Professional organizations, including the American Academy of Pediatrics, American Medical Association, and Society for Research in Child Development, have raised concerns about the potentially irreversible mental health effects of deportations and detentions on Latino or Latina youths. Objective: To examine how family member detention or deportation is associated with Latino or Latina adolescents' later mental health problems and risk behaviors. Design, Setting, and Participants: Survey data were collected between February 14 and April 26, 2018, and between September 17, 2018, and January 13, 2019, and at a 6-month follow-up from 547 Latino or Latina adolescents who were randomly selected from grade and sex strata in middle schools in a suburban Atlanta, Georgia, school district. Prospective data were analyzed using multivariable, multivariate logistic models within a structural equation modeling framework. Models examined how family member detention or deportation within the prior 12 months was associated with later changes in suicidal ideation, alcohol use, and clinical externalizing symptoms, controlling for initial mental health and risk behaviors. Exposure: Past-year family member detention or deportation. Main Outcomes and Measures: Follow-up reports of suicidal ideation in the past 6 months, alcohol use since the prior survey, and clinical level of externalizing symptoms in the past 6 months. Results: A total of 547 adolescents (303 girls; mean [SD] age, 12.8 [1.0] years) participated in this prospective survey. Response rates were 65.2% (547 of 839) among contacted parents and 95.3% (547 of 574) among contacted adolescents whose parents provided permission. The 6-month follow-up retention rate was 81.5% (446 of 547). A total of 136 adolescents (24.9%) had a family member detained or deported in the prior year. Family member detention or deportation was associated with higher odds of suicidal ideation (38 of 136 [27.9%] vs 66 of 411 [16.1%]; adjusted odds ratio, 2.37; 95% CI, 1.06-5.29), alcohol use (25 of 136 [18.4%] vs 30 of 411 [7.3%]; adjusted odds ratio, 2.98; 95% CI, 1.26-7.04), and clinical externalizing behaviors (31 of 136 [22.8%] vs 47 of 411 [11.4%]; adjusted odds ratio, 2.76; 95% CI, 1.11-6.84) at follow-up, controlling for baseline variables. Conclusion and Relevance: This study suggests that recent immigration policy changes may be associated with critical outcomes jeopardizing the health of Latino or Latina adolescents. Since 95% of US Latino or Latina adolescents are citizens, compromised mental health and risk behavior tied to family member detention or deportation raises concerns regarding the association of current immigration policies with the mental health of Latino and Latina adolescents in the United States.