Malignant growths of the sinuses are not common. Of almost 400 cases of all types and locations of malignant neoplasms collected by one of us (J. H. A.), the sinuses were involved in only 3 cases, in 2 of which the growth originated in the antrum and in 1 in the left sphenoid sinus. The occurrence of malignant tumors of the sphenoid sinus is sufficiently rare to warrant the publication of a case.Of 63 carcinomas and 7 sarcomas of the sinuses collected by Szende,2 none originated in the sphenoid sinus. According to Salinger,3 only 40 cases of malignant growths of the sphenoid sinus had been reported in the literature up to 1939. He pointed out, however, that as a rule carcinoma involving this sinus is diagnosed so late that it is difficult to determine exactly where the neoplasm arose. This suggests that a number of tumors which should have been diagnosed as cancer of the sphenoid sinus were called something else and vice versa. This would be true in the advanced stage of any malignant growth involving the base of the skull. One should, therefore, make no conclusive statements on the basis of the postmortem observations alone but should consider the clinical course and the direction of expansion of the neoplasm before arriving at a final diagnosis.report of a case History.-A white woman aged 30 underwent tests for duodenal ulcer in February 1939. During the course of this procedure she complained of "a tooth bothering her." The left upper first molar was removed, but a fistula developed into the left antrum. Roentgenograms of the sinus taken at that time revealed nothing abnormal. Severe pain, localizing about the left ear and the left mastoid region, continued throughout the summer.A submucous resection was done in September 1939, followed by a radical antrotomy a month later. Histologie examination of material obtained at the second operation revealed no neoplasm. One day after the radical antrotomy paralysis of the left sixth nerve suddenly developed. A caloric test and complete examination of the spinal fluid gave normal results.A blood count showed 7,700 white cells, 4,840,000 red cells and 13.3 per cent hemoglobin. In November 1939 the posterior half of the middle turbinate was removed; the posterior ethmoid cells were exenterated, and a large opening into the left sphenoid sinus was made.This sinus was observed to be filled with pus, and the mucosa was edematous. The results of biopsy of tissue removed from the sinus were negative for neoplasm. Two days later opening of the left mastoid revealed that the cells were intact but were lined with a grayish mucous membrane and contained serous exúdate.After the last operation the patient improved slightly. The pain was not quite so severe, and papilledema, seen prior to the operation, had cleared up. The visual field of the left eye showed a slight temporal defect. There were also some edema of the orifice of the eustachian tube and conductive deafness. During the following months the pain increased. Biopsy of material removed from the sphenoid sinus on two occas...