Pain behaviour can hamper rehabilitation. The aim of this study was to explore the phenomenon of pain behaviour in an unselected group of immigrant patients on >6 weeks of sick leave before and after a transcultural treatment programme in primary care. Anxiety about pain and pain behaviour-i.e. > or = 1.5 points on the University of Alabama in Birmingham (UAB) scale with scores of 0-10-were noted before and after treatment. The sex-adjusted odds ratios (OR) for pain behaviour, before and after the treatment, were calculated using logistic regression with 95% confidence intervals (95% CIs). Forty-nine men and 102 women having a mean age of 38 years participated. Their mean sick leave was 46 weeks. All reported psychosocial stress, one-quarter were depressed and social functioning was generally low. The pain was mostly caused by muscular insertion lesions (entesopathies). The frequency of pain behaviour and anxiety about pain declined after treatment (from 68% to 54% and from 76% to 50% respectively). Duration of full-time sick leave and among men also decreasing social functioning were correlated with the UAB score. Those who reported persistent anxiety about pain, or men who were depressed, had higher scores. Only persons on full-time sick leave >1 year had a significant OR for pain behaviour before treatment (OR 3.23; 95% CI 1.17-8.85, adjusted for sex). After treatment, only persons reporting persistent anxiety about pain showed a significant OR for pain behaviour (OR 3.05; 95% CI 1.49-6.23, adjusted for sex). In conclusion, pain behaviour was common in this group of immigrant patients < or = 45 years of age on long-term sick leave. Anxiety about pain and full-time sick leave for more than 1 year significantly predicted pain behaviour.