PURPOSE: Evidence linking screen time and physical activity with suicidality among adolescents is inconsistent. Our objective was to examine longitudinal associations between screen time and physical activity with suicidality among Danish adolescents. METHODS: Self-reported data on daily screen time and physical activity at age 11 was obtained from 28 613 adolescents (60% females) who participated in the Danish National Birth Cohort and linked to information on suicidality at age 18, based on self-reports and register data. Adjusted relative risk ratios (aRRR) were estimated using multinomial logistic regressions, while accounting for parental socio-demographics, psychiatric history and child risk behaviours. RESULTS: High levels of daily screen time (≥ 6 h) were reported by 6.9% and 12.6% of females and males, respectively. This was associated with suicidal ideation in females (aRRR:1.67, 95% CI:1.44-1.93) and suicide attempt in both sexes (females: aRRR:2.04 [1.51-2.75], males: aRRR:3.61 [1.89-6.89]) when compared to adolescents with <
2 h of daily screen time. Low levels of physical activity were reported by respectively 13.4% and 14.8% of females and males and was associated with increased risk of suicidal ideation (females: aRRR:2.18, [95% CI:1.94-2.44], males: aRRR:2.11 [1.83-2.43]) and suicide attempt (females: aRRR:2.27, [1.77-2.91], males: aRRR:2.49 [1.61-3.85]) when compared with those with the highest level. Independently of screen time level, males with low physical activity had higher risk for suicide attempt compared to males with a high level of physical activity. CONCLUSION: High levels of screen time and low levels of physical activity were associated with an increased risk of suicidality among adolescents.