OBJECTIVE To evaluate the refractive outcome using 5 intraocular lens (IOL) calculation formulas to determine which best predicts refraction after pediatric cataract surgery. METHODS The Hospital for Sick Children, Toronto, Ontario, Canada. METHODS This study comprised a review of the charts of 158 consecutive patients aged 2 to 17 years old who were operated on by 1 of 2 staff surgeons between May 1992 and April 2000. The surgeons performed a total of 206 cataract extractions with primary or secondary IOL implantation. The measured outcome was the actual refraction 2 to 6 months postoperatively versus the target refraction. Two regression formulas (SRK, SRK II) and 3 theoretical formulas (Holladay 1, Hoffer Q, SRK/T) were used to predict refractive outcome based on preoperative axial length, corneal curvature, IOL power, and the IOL A-constant provided by the manufacturer. RESULTS Forty-nine patients (59 IOL implantations) with available data 2 to 6 months after surgery were studied. Also analyzed were data from a subset of 31 patients (34 IOL implantations) with available data 2 to 3 months after surgery. There was poor to moderate agreement between the predicted and actual postoperative refractions using the SRK formula (intraclass correlation coefficient [ICC] = 0.50/0.04 [2- to 3-month follow-up/2- to 6-month follow-up]) and good or fair agreement using the other formulas (ICC from 0.60/0.24 for SRK II to 0.67/0.37 for Hoffer Q). The mean difference between the predicted and actual postoperative refractions with all formulas ranged from 1.06 to 1.22 diopters (D)/1.35 to 1.79 D (median 0.81 to 0.99 D/0.94 to 1.40 D; range 3.03 to 5.57 D/6.75 to 9.21 D). Using Holladay 1 and SRK, 9% to 18%/23% to 39% eyes were more than +/-2.00 D off the target outcome refraction. CONCLUSIONS All 5 IOL power calculation formulas were unsatisfactory in achieving the target refraction. This finding may have implications for predicting long-term outcomes, interpreting previous reports of refractive outcomes, and obtaining preoperative informed consent in a clinical setting.