The accuracy of IOL calculation using the SRK II formula was studied in 515 cataract extractions with posterior chamber IOLs. All excessively myopic patients (8 patients) and those where we had predicted an emmetropic postoperative result, from a consecutive series of 994 patients, were included. Preoperatively the patients were divided into different groups according to their refractive status and the mean postoperative refraction was calculated in each group. The mean postoperative refraction increased almost linearly with increasing myopic status. The emmetropic group achieved a mean postoperative refraction of -0.6 D, whilst in the most myopic group mean refraction was -1.8 D. We believe that the SRK II formula is inaccurate for myopic eyes, and that new formulas are needed, taking into account all those factors that make up the dioptric power of an eye.