Parents are important for the development and maintenance of regulatory control. The current longitudinal study examined associations between parental coercion and autonomy support and impulse control in 117 youth (ages 8-16; M age = 12.87, SD=2.53; 44% male) with Type 1 diabetes and explored whether youth negative affect mediated these associations. Parental coercion (but not autonomy support) was concurrently associated with lower impulse control and higher negative affect within individuals. Increases in youth negative affect partially mediated the within-person association between parental coercion and impulse control. These findings suggest that parent-directed interventions to reduce parental coercion may be most beneficial for impulse control if combined with youth-directed interventions to help them regulate negative affect. Replication of the current findings in a larger sample of youth with and without a chronic illness is needed to address the theoretical and empirical importance of negative affect as a potential mechanism through which parental coercion impacts youth impulsivity.