The number of patients with difficulty in resuming work after long-term sick leave has increased in several European countries including Sweden. The general aim of this study was a comprehensive description--based on multidisciplinary diagnostics and assessments--of patients with the common feature of marked difficulty in resuming working life after a long absence. A particular aim was to elucidate the possible effect of comorbidity on pain descriptors, disability, quality of life, assessed working ability and rehabilitation needs. Six hundred and thirty-five long-term sick leavers were referred from National Insurance Offices and consecutively accepted for investigation. Several self-report questionnaires were used. All patients were examined by three board-certified specialist physicians in psychiatry, orthopaedic surgery and rehabilitation medicine, respectively. Fifty-five percent of the patients had psychiatric-somatic comorbidity. The three most frequent combinations of diagnoses in the comorbidity group were fibromyalgia/myalgia and depressive episode, fibromyalgia/myalgia and recurrent depression, spinal pain and depressive episode, whereas the three most frequent in those with psychiatric diagnosis only were depressive episode, recurrent depression, phobias/anxiety. Differences in pain descriptors and in difficulties with activities were found among the three groups. All had lower health-related quality of life than references. Only one-sixth had no assessed working capacity and only 3% were assessed as able to resume work without rehabilitation; 80% were multidisciplinarily assessed as needing rehabilitation. Patients with psychiatric diagnoses, with or without concomitant somatic diagnoses, need medical rehabilitation or medical/vocational rehabilitation in combination to a greater extent than patients with somatic diagnoses only. This implies that medical rehabilitation programmes ought to adapt increasingly to the needs of patients with psychiatric-somatic comorbidity.