In order to evaluate risk factors for adhesive capsulitis of the shoulder ("frozen shoulder') a prospective study was carried out in neurosurgical patients, in whom there is a high incidence of capsulitis. Ninety-nine patients were admitted into the study, most of whom had surgical treatment for sub-arachnoid haemorrhage. Ninety-one patients (92 per cent) were followed up at six months, and of these 23 (25.3 per cent) had developed adhesive capsulitis, which was bilateral in three. Three patients developed the shoulder-hand syndrome. By comparing the patients with capsulitis at six months with those in whom no capsulitis was found, we were able to evaluate 28 possible risk factors (Appendix I). The subsequent development of adhesive capsulitis in our patients was associated with, (1) impairment of consciousness, (2) hemiparesis, (3) duration of post-operative intravenous infusion, (4) age, and (5) depressive personality. These five associations were statistically significant. Associations with phenobarbitine therapy and hysterical personality were suggested, but these did not reach statistical significance. Routine treatment with corticosteroids post-operatively did not prevent capsulitis.