An enduring tendency towards negative thinking is thought to increase vulnerability for future depression. However, it has not been possible to assess this tendency in non-depressed mood states. We examined if response latency to endorse dysfunctional attitudes is associated with depressive outcomes in a longitudinal study. A sample of young people at familial risk of depression (N = 252, aged 10–19, 56.3 % female) completed a computer-administered dysfunctional attitude scale. The main outcome measure was the difference in reaction time to agree versus disagree with dysfunctional attitudes. Cross-sectional differences between current and previous depression and no psychiatric disorder groups as well as longitudinal associations with depressive symptoms were examined. Young people with current and previous depression were quicker to agree with dysfunctional attitudes than those without disorder. In young people free from depressive disorder, faster agreements with dysfunctional attitudes were specifically associated with increased depressive symptoms over time. Self-reported dysfunctional attitudes did not differentiate the formerly depressed and no disorder groups and showed a longitudinal association with depressive symptoms for older adolescents only. Reaction time to endorse dysfunctional attitudes may indicate changes in affective processing that represent an early risk for future depression that is not indexed by self-report measures of negative thought.