Study objective: Despite its common clinical use, the range of normal pupillary size has been described only crudely. The objective of this report is to describe the distribution of normal pupillary sizes in 2 light conditions that are available in clinical settings. Methods: Pupillary size measurements were taken from healthy patients by the principal investigator using a modified Haab scale. Measurements were obtained in areas with fluorescent lighting with an intensity of between 2,700 and 5,400 lux and by using bright handheld light sources producing a light intensity of greater than 54,000 lux. The effect of varying the type of handheld device (otoscope, ophthalmoscope, or penlight) on mean pupillary size was analyzed on the basis of intervals calculated from the t distribution. Results: One hundred twenty-eight patients were enrolled, with a mean age of 35±9 years. The mean pupillary size in fluorescent light was 3.6±0.7 mm, and the mean size in bright light was 2.6±0.5 mm. Extreme values in fluorescent light were 2.6 mm (5th percentile) and 5.0 mm (96th percentile). Extreme values in bright light were 1.9 mm (3rd percentile) and 3.6 mm (96th percentile). The type of bright light source had no effect on pupillary size measurement. Conclusion: Pupillary sizes of greater than 5.0 mm or less than 2.6 mm are rare (<10%) in normal individuals in fluorescent lighting (2,700 to 5,400 lux), and sizes of greater than 3.6 mm or less than 1.9 mm are rare (<10%) in bright light. [Ann Emerg Med. 2003;41:247-250.]