OBJECTIVE The aim of the study was to evaluate factors possibly effecting the posterior capsule opacification (PCO), after extra-capsular cataract extraction with the posterior chamber intra-ocular lens (IOL) implantation. Age of patients, refractive errors, technique of cataract extraction, intra- and postoperative complications and coexisting diseases were taken into consideration. In 1992-98 posterior laser Nd:YAG capsulotomy was performed in 222 eyes of 222 patients (134 women and 88 men) previously operated in 1st and IInd Eye Clinic. PCO occurred in 5.8% patients, who underwent cataract extraction in this period, in 5.7% patients operated with phacoemulsification method and in 5.8% patients where extra-capsular cataract extraction with nucleus expulsion was performed. PCO was diagnosed in 12.7% patients at the age below 30, in 17% aged 31-40, in 7.8% aged 41-55 and in 5.1% patients older than 55 years. Among the patients, who developed PCO, in 6.3% myopia was present, in 8% primary open angle glaucoma, 16.6% were treated for diabetes mellitus. In 7.6% eyes the intra-operative cortical clean up was not efficient. CONCLUSIONS PCO occurred in young patients (under 40) twice as often as in the other groups of age. Technique of cataract extraction had an influence on the incidence of PCO as well.