Agency, communion, unmitigated agency (UA), and unmitigated communion (UC) are related to psychosocial health outcomes in nonclinical and medical populations. This study examined the relationship between these personality traits and emotional and interpersonal well-being, as up to 50% of women experience difficulties in psychosocial adjustment after being diagnosed with breast cancer. Seventy-four women newly diagnosed with breast cancer completed baseline assessment measures within 2 weeks prior to their first chemotherapy treatment or at the beginning of their hormonal therapy. Findings indicate that (1) agency and UA are important correlates of emotional and interpersonal adjustment and should be considered when attempting to identify women at high risk for psychosocial distress, and (2) UC deserves increased attention in behavioral medicine research, given its strong relationship with emotional distress in a breast cancer population. Thus, evidence continues to accumulate regarding the important relationship of these personality traits to psychosocial outcomes in medical populations.