One of the most exciting developments within postoperative pain research in recent years has been the introduction of Patient Controlled Analgesia (PCA). PCA is a technique in which patients self-administer small doses of opioids intravenously and it has been shown to be more effective than the conventional intramuscular injection method (IMI). However, PCA requires costly equipment and this necessarily places constraints on its availability. Therefore it is vital to ensure that the PCA facilities which are available are used as efficiently as possible. Essential to this is an understanding of the categories of patients for whom it will be most effective. At present the basis of selection of patients for PCA is often unclear. Frequently anaesthetists use the extent of trauma as a guide, although there is no evidence that this is the most effective strategy. Moreover, it ignores numerous factors which empirical research has shown to influence the experience of postoperative pain. These include state and trait anxiety, neuroticism and coping style. Until now their importance has only been investigated within the IMI analgesic regime. The present thesis remedies this omission by investigating pain/personality relationships under both PCA and IMI regimes. A particular interest was the identification of ways of detecting the patients who would benefit most from the use of PCA in terms of personality profiles. This study investigated whether knowledge of the patient characteristics of state anxiety and trait anxiety, neuroticism and coping style can be used to predict which patients will benefit the most from PCA. This research involved two main studies, in which a sample of 164 adult female and male patients undergoing major elective surgery were preoperatively assessed in terms of anxiety, neuroticism and coping style. Postoperatively they were allocated to either PCA or IMI analgesic regimes and their pain experience was assessed at 6,18 and 24 hours after surgery. The data were analyzed using Pearson's Correlations, T tests, Analysis of Variance and Multiple Regression. The findings revealed that state anxiety and coping style were significant predictors of postoperative pain for PCA as well as IMI regimes. Patients using PCA experienced significantly better pain relief than did their IMI counterparts. However, it was the patients with high levels of state anxiety using PCA who benefited the most. The superior pain control of PCA was not found to be related to the presence of the technically sophisticated PCA machine. PCA was also associated with a reduction in the length of hospital stay and a saving of nursing time on the ward. Patients had positive reactions about being in control of their pain relief, whilst staff felt that patient control was beneficial. They were also impressed by the time saving element of PCA. The implications for the management of post operative pain and the financial saving are considered.