Links between children's attachment security with mothers and fathers, assessed in Strange Situation with each parent at 15 months (N = 101), and their future behavior problems were examined. Mothers and fathers rated children's behavior problems, and children reported their own behavior problems at age 8 (N = 86). Teachers rated behavior problems at age 6½ (N = 86). Insecurity with both parents had a robust effect: “Double-insecure” children reported more overall problems, and were rated by teachers as having more externalizing problems than those secure with at least 1 parent. Security with either parent could offset such risks, and security with both conferred no additional benefits. High resistance toward both parents in Strange Situation may confer “dual risk” for future externalizing behavior.