The study included 188 patients, in which a posterior chamber intraocular lens was implanted after extracapsular cataract extraction. After modifications of the intraocular lens constants (SRK formula and SRK II formula) and correction of the axial length measurements (Colenbrander-Hoffer formula) had been made, the mean differences between the actual postoperative spherical equivalent and that predicted by the three formulas were -0.23D, -0.22D and -0.46D, respectively. More than +/-1.0D deviation from the predicted postoperative refraction occurred in about one-third of the cases. Inter-observed discrepancy regarding the accuracy of the preoperative measurement of the ocular axis length is suggested to be the main cause of unpredicted postoperative refractive errors.