This study of 166 best friend dyads (M = 10.88 years) examined (a) whether children and their best friends were similar in social information processing (SIP) that pertained to two relationship contexts (unfamiliar peer, friend); (b) the associations between children's and their best friends' SIP and friendship quality and conflict ratings; and (c) the relations between SIP similarity and dyadic friendship ratings. Analyses revealed a greater number of similarities for the "friend context" (hypothetical scenarios involving each other) than the "unfamiliar-peer context" (scenarios involving unknown peers). Significant relations were found, in both relationship contexts, between children's angry reactions, appeasement coping, and friendship quality ratings, and between external blame attributions and appeasement coping, and conflict ratings. A number of significant associations between similarity, or lack thereof, in "aggression"-related SIP and friendship qualities suggest that the extent to which children and their friends are similar in aggression-related SIP may explain some variability in the quality of friendships. (Contains 1 figure and 4 tables.)