Purpose: To study the correlation between posterior capsule opacification (PCO) and intraocular straylight and visual acuity. Design: Prospective noninterventional study. Methods: We measured visual acuity (VA), logarithm of minimal angle of resolution (logMAR) and intraocular straylight (C-Quant straylight parameter log[s]) under photopic conditions before and 2 weeks after YAG capsulotomy in 41 patients (53 eyes) from the Centro de Oftalmologa Barraquer in Barcelona and the University Eye Clinic, Paracelsus Medical University in Salzburg. Photopic pupil diameter was also measured. To document the level of opacification, pupils were dilated and photographs were taken with a slit lamp, using retroillumination and the reflected light of a wide slit beam at an angle of 45 degrees. PCO was subjectively graded on a scale of 0 to 10 and using the POCOman system. A multiple regression analysis was performed to evaluate factors that influence straylight after capsulotomy. Results: Straylight correlated well with retroillumination and reflected-light PCO scores, whereas VA only correlated with retroillumination. Both VA and straylight improved after capsulotomy. Straylight values varied widely after capsulotomy. Multiple regression analysis showed that older age, large ocular axial length, hydrophobic acrylic intraocular lenses (IOLs), and small capsulotomies are factors that increased intraocular straylight. Conclusion: Intraocular straylight is a useful tool in the assessment of PCO. It correlates well with PCO severity scoring methods. When performing a posterior capsulotomy, factors such as age, IOL material, axial length, and capsulotomy size must be taken into consideration, as they influence intraocular straylight. © 2010 Elsevier Inc. All Rights Reserved.