Research findings over the last 20 years show that critical care nurses (CCNs) continue to underestimate and under medicate their patients' pain, despite an allegedly strong commitment to pain relief. This literature review investigates the determinants of CCNs' pain assessment and management behaviours. Fishbein and Ajzen's theory of reasoned action' and Ajzen's theory of planned behaviour have been used as models to facilitate understanding of this phenomenon. Fishbein and Ajzen highlight attitudes, beliefs, subjective norms and the motivation to comply to the anticipated expectations of significant others as the determinants of intention to perform behaviour. Attitudinal barriers, knowledge deficits and the influence of peers affect CCNs' pain management behaviours, resulting in inadequate pain assessment and management practices. CCNs' attitudes about narcotic analgesia and how this interacts with gender, age and culture are also explored. Through an analysis of the behavioural determinants following the models described by Fishbein and Ajzen, strategies can be formulated to address CCN deficiencies, improve patient outcomes and satisfaction with nursing care and CCN fulfilment. Cervantes was quoted as saying "It's a long way from saying to doing". This report aims to improve on this idea.