The purpose of this study was to examine the difference between subjective refraction and autorefraction for different age groups. We call the difference (autorefraction minus subjective refraction) the excess of autorefraction over subjective refraction or the autorefractive excess. Five age groups of 50 subjects each were used. Subjects in group 1 were aged between 1 and 10 years, group 2 between 11 and 20 years, group 3 between 21 and 30 years, group 4 between 31 and 40 years, and group 5 consisted of subjects over 41 years of age. Automatic refraction was performed with an Allergan Humphrey model 580 autorefractor. The data were analyzed using recently developed statistical methods for the analyzing of dioptric power. These methods include the use of the coordinate vector h as a representation of dioptric power. The results indicate that there is a statistically significant mean autorefractive excess and that the mean is different for different age groups. The behavior of the left and right eyes appears to be essentially the same. In terms of vector h the mean autorefractive excess for both the left and the right eyes of group 1 (1 to 10 years of age) is approximately (-0.25 0.00-0.43)'. It increases by roughly delta h = (0.10 0.00 0.10)' per decade. In more conventional terms the nearest equivalent sphere of the mean excess for group 1 is approximately -0.34 D for the right and for the left eyes. The mean autorefractive excess for group 1 is approximately -0.25 -0.18 x 180. The astigmatic component appears to be the same for all age groups, whereas the spherical component increases by approximately 0.1 D per decade. The standard deviations of the autorefractive excesses are relatively large for components h1, and h3 of h: they were between approximately 0.4 and 0.7 D, possibly decreasing slightly with age. The standard deviation of h2 remains at 0.2 D or less for all age groups. The greatest variation of autorefractive excess appears to be approximately in the spherical direction in symmetric dioptric power space and appears to be less for the older age groups than the younger age groups.