BACKGROUND AND PURPOSE: Unilateral gaze palsy associated with internuclear 
ophthalmoplegia (INO), i.e., one-and-a-half syndrome, is well known. Exotropia 
can also be associated with INO, but it has been reported only rarely. We sought 
to determine the frequencies and courses of gaze palsy and exotropia in INO.
METHODS: Patients hospitalized with acute-onset INO during the period January 
2009 through December 2013 were identified from our clinical registry. 
Associated gaze palsy and exotropia were evaluated in the identified patients.
RESULTS: Twenty-five patients with unilateral INO and 7 patients with bilateral 
INO were included in this study. Of the 25 patients with unilateral INO, 4 
(16.0.0%) had ipsilateral gaze palsy (one-and-a-half syndrome), 8 (32.0%) had 
exotropia (non-paralytic pontine exotropia), and 6 (24.0%) had both ipsilateral 
gaze palsy and exotropia (paralytic pontine exotropia). Six (85.7%) of the 7 
patients with bilateral INO had exotropia. The gaze palsy persisted more than 1 
week in 40.0% of patients, whereas the exotropia disappeared within 1 week in 
92.9% of patients when the INO was unilateral.
CONCLUSION: Exotropia is not uncommon in the acute stage of INO. However, it is 
often overlooked because of its short duration.