The relationship between health locus of control and functioning in Chronic Fatigue Syndrome (CFS) was investigated. The hypothesis was that an internal health locus of control would be associated with less impairment in functioning than other dimensions of health locus of control. Prior research undertaken into CFS has been inconsistent in its finding's and it continues to be an area of controversial interpretations. A repeated measures design was used, 74 people participated at the initial stage of the study and 67 people participated in the second stage. The Functional Limitations Profile was used to assess levels of impairment. The Multidimensional Health Locus of Control was used to identify types of health locus of control orientation, and the Shapiro Control Inventory was used to establish a clearer picture of control issues. Correlations and t-tests were used to investigate the relationship between health locus of control and functioning. The results of these analyses indicated that an internal health locus of control was positively related to functioning. Multiple regression analysis was performed and showed that an internal health locus of control could successfully predict functioning measured at the second stage of the study. An unexpected discovery was that a doctor's health locus of control impacted negatively on functioning. The Shapiro Control Inventory revealed that the CFS sample fell within the normal range in the majority of control areas, but was outside the normal range in only six of the 23 control areas. These findings indicated that health locus of control does play an important role in CFS. It was therefore concluded that increasing a patient's sense of control and reflecting this in the treatment regime of CFS would aid recovery.