Objective: We examined the links of supportive and conflictual peer interactions to mood and self-care via ecological momentary assessment. Method: Adolescents with Type 1 diabetes (n = 167, 49% female) recruited between 2018 and 2021 were prompted 8 times a day for 8 days to complete brief surveys that measured perceived social interactions, affect, and self-care. Results: Cross-sectional analyses revealed between- and within-person (WP) links of peer support to positive mood and conflict to negative mood. Between-person peer support was linked to healthy self-care, but WP support was not. Lagged analyses showed conflictual interactions were associated with self-care decline. There was some evidence that females did not benefit as much from support and were more bothered by conflict than others. Conclusions: Results underscore differences in between- and WP links of social interactions to health. Individual differences in support were more influential than conflict, but conflictual interactions had more momentary effects than supportive interactions. Objetivo: Examinamos los vínculos entre las interacciones de apoyo y conflictivas entre pares con el estado de ánimo y el autocuidado a través de una evaluación ecológica momentánea. Métodos: A los adolescentes con diabetes tipo 1 (n = 167, 49% mujeres) reclutados entre 2018 y 2021 se les pidió 8 veces al día durante ocho días que completaran breves encuestas que medían las interacciones sociales percibidas, el afecto y el autocuidado. Resultados: Los análisis transversales revelaron vínculos entre y dentro de las personas entre el apoyo de los pares y el estado de ánimo positivo y el conflicto con el estado de ánimo negativo. El apoyo entre pares se vinculó con un autocuidado saludable, pero el apoyo intrapersonal no. Los análisis rezagados mostraron que las interacciones conflictivas estaban asociadas con una disminución del autocuidado. Hubo cierta evidencia de que las mujeres no se beneficiaban tanto del apoyo y les molestaban más los conflictos que otras. Conclusiones: Los resultados subrayan las diferencias en los vínculos entre las interacciones sociales y la salud entre personas y dentro de ellas. Las diferencias individuales en el apoyo fueron más influyentes que el conflicto, pero las interacciones conflictivas tuvieron efectos más momentáneos que las interacciones de apoyo. Public Significance StatementSubstantive contributions to research on Type 1 diabetes are made by focusing on peer relationships, examining both support and conflict, testing gender moderation, and employing a design that examines proximal links of social interactions to health. Between-person and within-person support and conflict were related to mood, but only between-person support was related to self-care. A key longitudinal finding showed within-person peer conflict was linked to declines in self-care over time.