Family environment is a pathogenic factor of borderline personality disorder (BPD). However, the personality traits of patients with BPD and their parents have never been assessed using the same instrument and then examined for relationships. In the present study, we explored the temperament and character traits of BPD patients and their parents to investigate possible interactions. In total, 56 patients with BPD and their parents were evaluated with the Temperament and Character Inventory (TCI) and compared with 53 control families. Discriminant and correlation analyses indicated that subjects with BPD displayed higher levels of novelty seeking, harm avoidance, and self-transcendence and lower levels of self-directedness than control subjects. Their fathers displayed higher levels of novelty seeking and lower levels of persistence and self-directedness, and their mothers displayed lower levels of self-directedness compared with levels in control parents. In BPD families, temperament and character traits displayed high levels of discriminatory power. Novelty seeking in offspring with borderline personality disorder was significantly correlated with their mothers' novelty seeking and their fathers' self-transcendence. Self-directedness in borderline offspring was significantly correlated with both their mothers' and fathers' novelty seeking, and their self-transcendence was significantly correlated with their mothers' novelty seeking and harm avoidance. The different correlational pattern for borderline and control families is discussed. Characteristic personality patterns were found in BPD offspring and in both parents. The relationship between personality traits of borderline offspring and those of their parents may be related to both genetic transmission and family dynamics. Ramifications for treatment are discussed.