This was a study of acute cluster endophthalmitis along with clinical features, culture results, and visual outcomes of 10 eyes of 10 patients after intravitreal injection of Avastin (bevacizumab) in one sitting from a single vial.Retrospective review of intravitreal injection of 1.25 mg/0.05 ml bevacizumab that was given to 10 eyes of 10 patients on the same day from a freshly opened vial. All patients manifested with endophthalmitis the next day. Vitreous tap for direct smear and culture was done. Intravitreal antibiotics and steroids were injected and appropriate treatment begun. The injection vial of the same batch was sent for VITEKTM identification and antimicrobial susceptibility of isolates.Endophthalmitis presented within 24 h of intravitreal injection. There was a remarkable absence of posterior pupillary synechia. Two cases were culture-positive (20%), showing pseudomonoid growth. The vial of the same batch revealed a pseudomonoid bacilli Stenotrophomonas maltophilia using VITEKTM, which was resistant to multiple drugs. Hence, the contaminated vial was identified as the source of infection in our case. Among 10 patients, two underwent pars plana vitrectomy. Visual acuity returned to preendophthalmitis levels in 9/10 eyes after 1 month. One patient was lost to follow-up. Late complications included retinal detachment in one case and neovascular glaucoma in another.Early recognition and treatment are key factors in improving outcomes. Causative etiology could be microbial contamination of the drug vial. S. maltophilia should be considered a pathogenic organism of postintravitreal endophthalmitis.