Given the suggestion of a reciprocal relationship between sleep and pain and the recognition of sleep as an important parameter in determining quality of life, there is increasing research interest in sleep disturbance linked to chronic pain. The present study aimed to provide an estimate of the prevalence of 'clinical insomnia' in patients attending a specialist pain clinic and identify factors associated with it. Seventy chronic back pain patients and 70 gender- and age-matched pain-free controls completed a set of questionnaires measuring sleep (Insomnia Severity Index; ISI), pain (Short-Form McGill Pain Questionnaire) and a selection of general and specific psychological variables (Hospital Anxiety and Depression Scale, Short Health Anxiety Inventory). Scores suggestive of clinical insomnia (ISI > or = 15) were noted in 53% of chronic pain patients, when compared with only 3% in pain-free controls. Significant positive correlations with insomnia severity were detected for all six variables of interest (pain intensity, sensory pain ratings, affective pain ratings, general anxiety, general depression and health anxiety). Affective pain ratings and health anxiety were the best predictors of insomnia severity in this sample, accounting for 30% of the total variance, even when present pain intensity was controlled for. Affective pain remained as a significant predictor of insomnia severity when both the effect of pain intensity and the effects of anxiety and depression were controlled for. Future research should consider investigating the role of pain appraisal and health anxiety in the development and manifestation of insomnia concomitant to chronic pain.