We examined the test-retest reliability of visual acuity in 18 children referred to the Hospital Eye Service with reduced vision. Unaided distance acuities were recorded, using logarithmically scaled letter charts, on two occasions separated by an interval of one week during which no clinical intervention took place. Coefficients of repeatability were found to be +/- 0.25 and +/- 0.21 log units in left and right eyes, respectively. A further analysis of 14 subjects' data each of whom had one eye with consistently poorer acuity in both test sessions yielded coefficients of repeatability of +/- 0.15 and +/- 0.22 log units in, respectively, the better and poorer eyes. The reliability of visual acuity recorded in the better eye closely approximates to that previously found in normal adults, whilst that of the poorer eye appears more comparable to that of adult clinical populations.