Two hundred thirty-two patients with nasopharyngeal carcinoma were evaluated for serous otitis media (SOM) at diagnosis. The diagnosis of SOM required the detection of effusion behind the tympanic membrane in association of air-bone gap of 10 dB or more in pure tone audiogram. These patients were also evaluated by computed tomography for the degree of tumor extension. By stepwise logistic regression analysis, the degree of paranasopharyngeal extension of tumor, erosion of petrous temporal bone, and the obliteration of pharyngeal recess were significantly related to the development of SOM, but sex and age were not. The findings of computed tomography may influence the plan of management for SOM in patients with nasopharyngeal carcinoma at diagnosis.