To assess the safety and effectiveness of immediately sequential (ISBCS) versus delayed sequential (DSBCS) bilateral cataract surgery. Multiple clinics, Canary Islands, Spain. Multicenter randomized clinical trial. Patients with cataracts requiring bilateral surgery were randomized to ISBCS or DSBCS. Outcome measures were the incidence of intraoperative and postoperative surgical complications, corrected and uncorrected visual acuities, and self-perceived visual function (VF-14 questionnaire). All outcomes were measured 30 days postoperatively. Self-perceived visual function was also assessed after 1 year. Data were analyzed with repeated measures to assess temporal effects on surgical complications, visual acuity, and function. Effect size was also estimated for self-perceived visual function. There were no differences in intraoperative or postoperative surgical complications, visual acuity 30 days postoperatively, or self-perceived visual function after 1 year between the 2 techniques. Effect size for visual function 30 days postoperatively was moderate in the ISBCS group (n = 834) and small in the DSBCS group (n = 780). This difference disappeared at 1-year follow-up after second-eye surgery in the delayed group. There were no relevant surgical complications in 1614 operated eyes and no significant difference in surgical complications, visual acuity, or long-term self-perceived visual function between ISBCS and DSBCS. These safety and effectiveness outcomes were related to careful patient selection, surgical expertise, and the systematic use of standardized surgical guidelines to ensure aseptic and independent surgery in each eye.