PURPOSE: To measure accurately the amount of cyclotorsion. METHODS: A horizontal light beam of the slit lamp is projected on the retina, crossing the fovea. The slit light will normally cross between the middle and lower thirds of the disk. Cyclotorsion of the eye will cause the horizontal slit- light beam to be projected onto a different part of the disk. The slit light is then tilted by the scale mark on the slit lamp in such a way that the slit light is crossing the fovea and the physiologic area on the disk. RESULTS: The amount of slit-lamp tilt needed is obtained from the scale mark on the slit lamp. This test correlated well with other tests used for the appreciation of cyclotorsion: the Maddox double rod test and indirect ophthalmoscopy. CONCLUSION: A simple method for measuring ocular cyclotorsion is described.