This study investigated the relative rates of personality disturbance in chronic fatigue syndrome (CFS). Individuals who met the CDC criteria for CFS were compared to two other fatiguing illness groups, mild multiple sclerosis and depression, as well as sedentary healthy controls. Subjects were administered a structured psychiatric interview to determine Axis I psychiatric disorders and two self-report instruments to assess Axis II personality disorders and the personality trait of neuroticism. The depressed group had significantly more personality disorders and elevated neuroticism scores compared with the other three groups. The CFS and MS subjects had intermediary personality scores which were significantly higher than healthy controls. The CFS group with concurrent depressive disorder (34% of the CFS group) was found to account for most of the personality pathology in the CFS sample. The results are discussed in the context of the relationship between personality variables and fatiguing illness.