We observed a unilateral free-floating vitreous cyst in a 6-year-old boy. The ophthalmologic examination was otherwise normal. The cyst, which was pigmented, had a diameter of approximately of 2.5 mm and was localized in the anterior vitreous of the left eye. In its movements it occasionally affected the visual axis, causing only transient and sporadic blurring of vision. Visual acuity in the affected eye was equal to that in the other eye (20/20). Follow-up is by periodic examinations.