PURPOSE: To present a cluster of cases of corneal edema occurring after phacoemulsification. SETTING: Regional hospital in rural Australia. METHODS: This retrospective case series comprised 12 patients from a single surgical list comprising 19 cases who developed persistent corneal edema after having phacoemulsification. RESULTS: After 6 months, the edema improved in 1 patient. Inadvertent intraocular use of balanced salt solution (BSS) preserved with benzalkonium chloride was found to be the cause of this serious complication. CONCLUSIONS: Benzalkonium chloride in concentrations commonly used extraocularly is highly toxic to the corneal endothelium. Every possible safeguard should be taken to prevent inadvertent intraocular use of such preserved solutions.