This report describes three cases of undifferentiated small cell carcinoma of the urinary bladder. Their light microscopic appearance is closely akin to the small cell carcinoma of lung. The neoplastic cells exhibit few cytoplasmic dense core neurosecretory granules ultrastructurally and immunoreactivity to enolase. Two patients manifested clinically hypercalcemia which is rare in small cell carcinoma in general and, to the best of our knowledge, has not been described in association with bladder small cell carcinoma. Cancer 56:2530-2533, 1985. MALL CELL CARCINOMAS are being reported with in-S creasing frequency in different expulmonary locations , e.g., esophagus, breast, head and neck regions, skin, and prostate.la2 These tumors share histologic and ultra-structural features with small cell carcinoma of the lung, including the presence of small numbers of neurosecretory type granules. The latter have been considered as a common denominator of neoplasms of the APUD system, a unifying concept that has proved useful in understanding ectopic hormone production in malignancy. Carcinoma of the urinary bladder containing neurosecretory granules has also been described by Cramer et aL3 in a 69-year-old man who presented with symptoms of urinary im-tability, hematuria, and hypophosphatemia. The latter resolved spontaneously after conservative surgical treatment and there was no recurrence or metastasis over a follow-up period of 14 months. Since then, there are only four other cases reported in the literat~re.~.~ Recently, Kim and associates have also described two cases of urinary bladder small cell carcinoma which did not reveal ultra-structural features of neuroendocrine cells.s The following is a report of three additional cases of this neoplasm, two of which are associated with hyper-calcemia. Case Reports Case 1 A 64-year-old man presented with acute painless hematuna. Past history was unremarkable except for mild essential hyper-tension. Initial x-ray studies and laboratory tests were within normal limits. Cystoscopy revealed a 2 c m polypoid tumor on the left posterolateral wall of the urinary bladder. This was re-From the Laboratory and Medical Services, Edward J. Hines, Jr. Vet-Address for reprints: Dr. Cesar V. Reyes, 578/113, Edward J. Hines, Accepted for publication February 13, 1985. erans Administration Hospital Hines, Illinois. Jr. Hospital, Hines, IL 60141. sected and fulgurated. Microscopically the lesion was an undif-ferentiated small cell carcinoma (Figs. 1 and 2) with superficial muscle invasion. Electron microscopy of representative tumor cells demonstrated the presence of small numbers of neurose-cretory type granules located in cytoplasmic extensions and sub-plasmalemmal positions. The cells were also immunoreactive to enolase but not to prostatic acid phosphatase and prostatic FIG.