The purposes of this study were to determine if there were significant differences in the mood states of oncology outpatients who had cancer-related pain and those who were pain free, and to evaluate the relationships between pain intensity and duration and mood states in those patients with pain. Two hundred (54.2%) patients experienced cancer-related pain during the previous month and 169 (45.8%) patients were pain free. Those patients who experienced cancer-related pain scored significantly higher on all of the subscale scores of the Profile of Mood States, except vigor, and had a significantly higher total mood disturbance (TMD) score than did pain-free patients. In addition, the subscale scores of tension, depression, anger, fatigue, confusion, and TMD scores were moderately correlated with increases in pain intensity. Also, depression, fatigue, confusion, and TMD scores were moderately correlated with increasing duration of pain. These data suggest that there is a relationship between pain and mood in oncology outpatients and that health-care professionals need to assess for mood disturbances in this population and develop appropriate treatment strategies.