This study will enroll individuals with high levels of hostility. At an initial screening visit, potential participants will partake in interviews and complete questionnaires to assess hostility levels. Eligible participants will then undergo 24-hour continuous electrocardiogram (ECG) monitoring and will complete questionnaires about their surroundings and any hostility experienced during the 24-hour period. They will also undergo psychophysiological testing, in which responses to a variety of stress-inducing situations will be monitored. Participants will then be randomly assigned to either a 12-week CBT hostility reduction treatment program or a 12-week wait list control group. Participants in the CBT program will attend weekly 75-minute therapy sessions, which will focus on relaxation, stress reduction, behavior management, and development of social, communication, and coping skills. Hostility levels will be documented each day in a diary. Participants in the wait list control group will not take part in any therapy sessions for the initial 12 weeks. At Week 12, baseline evaluations will be repeated for all participants. The waitlist control group will then begin the 12-week CBT program. All participants will attend a 6-month follow-up visit for repeat testing.