This study compares the predictive accuracy of the SRKII formula for groups with average axial length and long eyes. 344 eyes which underwent cataract extraction with implantation of a posterior-chamber intraocular lens were included in the survey; 246 eyes had an average axial length (22.0-24.49 mm), and 98 eyes had an axial length of more than 24.50 mm. Mean absolute errors were 0.26+/-0.68 dpt in the first group and 1.16+/-1.78 dpt in the second group. 94.3% of the average eyes were within 1.0 dpt of the expected refraction, 98.8% within 2.0 dpt, whereas in the long-eye group 58.2% were within 1.0 dpt and 84.7% within 2.0 dpt. The results show that the SRKII formula performed credibly in average-length eyes; in the long eyes the ratio of large refractive deviations was greater than that of the other group.