Pneumocystis carinii pneumonia complicating somatostatin therapy of Cushing's syndrome in a patient with metastatic pancreatic islet cell carcinoma and Zollinger-Ellison syndrome. Described is the case of a 73-yr-old woman with metastatic pancreatic islet carcinoma that manifested initially as Zollinger-Ellison syndrome followed by onset of endogenous Cushing's syndrome, who developed Pneumocystis carinii pneumonia while on therapy with a long-acting somatostatin analog. Although P. carinii pneumonia has been observed in patients with Cushing's syndrome associated with other conditions, this is the first reported case in a patient with Zollinger-Ellison syndrome. Heightened awareness of the possibility of opportunistic infections in patients receiving somatostatin therapy for Cushing's syndrome of any cause, particularly Zollinger-Ellison syndrome, may be warranted. 