Purpose: To prospectively compare the scotopic pupil size between emmetropes and myopes using a Colvard pupillometer. Methods: The pupil diameters of 55 normal subjects and 55 healthy myopic subjects were measured with the Colvard pupillometer in a low-light situation that simulated the level of light encountered while driving at night. Results: The mean (± SD) age of the emmetropic subjects was 30.78 years ± 10.03 (range, 18-54 years) and the mean (± SD) age of the myopic subjects was 27.35 years ± 8.43 (range, 21-52 years). The mean (± SD) scotopic pupil diameter was 6.46 ± 0.90 mm (range, 4.5-8.0 mm) in the emmetropic group and 6.98 ± 0.67 mm (5.5-8.5 mm) in the myopic group. The unpaired Student t-test showed that the difference in the scotopic pupil diameter between emmetropes and myopes was statistically significant (P = .0001). Conclusions: The mean scotopic pupil diameter in myopes was larger than that in emmetropes. Therefore, a large ablation zone of the cornea or an appropriate optical size of the phakic intraocular lens should be considered in refractive surgery. Preoperative scotopic pupil measurements may be necessary in all refractive patients. © 2002 Japanese Ophthalmological Society.