We examined how the real-life dyadic friendships of 87 children with ADHD and 46 comparison children (76 % boys) aged 7–13 years evolved during a 6-month follow-up period. The methods included friendship quality self-report measures and direct observation of friends’ dyadic behaviors in three structured analogue tasks. At Time 2, the friends of the participants with ADHD reported less positive friendship quality and more conflict with their friends than at Time 1. They were also considerably less satisfied with their friendship than 6 months prior. In contrast, the friends of comparison children reported fewer negative friendship features, more positive friendship features and a slightly greater friendship satisfaction than at Time 1. In sharp contrast with the invited friends’ reports, referred children with ADHD did not report deterioration in their friendship quality over time. Unlike comparison children who significantly reduced violations of game rules between Time 1 and Time 2, children with ADHD broke more game rules during the same period. In negotiating with friends, comparison children, but not children with ADHD, reduced the number of self-centered and insensitive proposals at Time 2. Controlling for Time 1 variance, violations of game rules and a self-centered, insensitive negotiation approach predicted deterioration in friendship quality for children with and without ADHD over time.