I reviewed retrospectively the records of 147 consecutive patients who had superior oblique palsy. Of the 147 patients, 28 had bilateral superior oblique palsies, and in nine of the 28 the involvement was so asymmetric that the palsy in the lesser affected eye was either completely masked or almost masked preoperatively. Relying on preoperative diagnostic criteria such as the presence of bilateral objective torsion, cover testing in the oblique fields of gaze, size of the subjective cyclotropia, amount of the "V" shift, and subjective symptoms, all nine patients underwent bilateral surgery at the time of their initial operation and obtained satisfactory results. No patient was later found to have bilateral masked superior oblique palsy after unilateral surgery.