Purpose: To assess the accuracy of using axial length measurement obtained prior to vitrectomy with silicone oil internal tamponade in predicting the intraocular lens power and postoperative refraction in patients operated later on with combined cataract extraction, silicone oil removal and intraocular lens implantation. Methods: In this prospective study, the axial length was measured preoperatively in 25 patients requiring vitrectomy with silicone oil tamponade. Keratometry readings were obtained before cataract surgery and the intraocular lens power was calculated using the SRK II formula. Postoperative refraction was aimed at emmetropia. Phacoemulsification with silicone oil removal through a posterior capsulotomy was performed in all cases. Intraocular lens was implanted in 20 cases. Postoperative refraction was considered stable after a minimum of 3 months follow-up and the data were obtained for statistical analysis. Results: two cases had recurrence of retinal detachment within three months postoperatively and were excluded from statistical analysis. The mean postoperative refraction (spherical equivalent) for the whole group (23 cases) was -1.43±1.51 diopters. In the intraocular lens group (19 cases), the mean postoperative refraction was -1.97±0.95 diopters. 18 cases (94.74%) had myopic postoperative refraction within the range of three diopters of the predicted refraction and one case had -4.00 diopters. In the aphakic group (4 cases) the mean postoperative refraction was +1.00±0.82 diopters. three cases were hyperopic and one case was emmetropic. Conclusion: Preoperative axial length measurement in cases requiring vitrectomy with silicone oil tamponade results in mild degrees of postoperative myopia within three diopters in most of the cases after cataract extraction and silicone oil evacuation. Using this technique helps to overcome the problems of intraocular lens power calculations in silicone oil filled eyes.