Three patients with Parkinson's disease are described who developed pericardial, retroperitoneal, and pleural fibrosis associated with pergolide treatment. Surgical intervention was required in all three cases, either to reach a tissue diagnosis or for potentially life threatening complications. Symptoms emerged on average 2 years after the institution of treatment, and were sufficiently non-specific to cause significant delays in diagnosis in all cases. The erythrocyte sedimentation rate (ESR) was raised in the two patients in whom it was measured. Serosal fibrosis is a rarely reported adverse effect of pergolide treatment, although it is well described with other dopamine agonists. We suggest that patients with Parkinson's disease who receive pergolide treatment should be regularly monitored for the development of such complications.