Purpose: To investigate binocular function in bilateral and unilateral implantation of the refractive multifocal intraocular lens (IOL).Setting: Department of Ophthalmology, Musashino Red Cross Hospital, Tokyo, Japan.Methods: Sixty-six eyes of 40 patients were enrolled in this retrospective study. Twenty-six were implanted bilaterally and 14 were implanted unilaterally with the 3-zone refractive multifocal IOL. Distance visual acuity, near visual acuity, and contrast sensitivity were measured monocularly and binocularly. Stereopsis, aniseikonia, and the use of spectacles were also evaluated.Results: There were no significant between-group differences in monocular and binocular visual acuity. In the bilateral group, 85% had 60 seconds or more of stereopsis; in the unilateral group, 43% had the same level of stereopsis (P = .009). Ninety-two percent and 21%, respectively, had no aniseikonia (P = .001), and 89% and 50%, respectively, did not use spectacles (P = .012). In the unilateral group, in 4 of 5 cases in which surgery was performed in the dominant eye, spectacles were not required; in 9 cases in which surgery was performed in the nondominant eye, 78% used spectacles for reading (P = .063).Conclusions: Bilateral implantation of the multifocal IOL appeared to lead to better results than unilateral implantation. However, our results suggest that the patient may be satisfied with unilateral implantation when it is performed in the dominant eye. [Copyright &y& Elsevier]