We analyzed the likelihood of rehospitalization for endophthalmitis in 338,141 Medicare beneficiaries over age 65 years who were admitted to US hospitals for cataract extraction in 1984. This cohort represents approximately one half of all persons who underwent cataract extraction under the Medicare program in 1984. Extracapsular extraction was performed in 195,587 (58%) of cases, intracapsular cataract extraction in 99,971 (30%), and phacoemulsification in 28,474 (8%). The risk of rehospitalization for endophthalmitis in the year following surgery was 0.17% for intracapsular cataract extraction compared with 0.12% for extracapsular extraction or phacoemulsification (P less than .002). The risk of endophthalmitis at 1 month was higher for intracapsular cataract extraction than for extracapsular extraction or phacoemulsification (0.11% vs 0.085%), although the difference did not reach statistical significance. Cataract surgery accompanied by anterior vitrectomy increased the 1-month risk of rehospitalization for endophthalmitis to 0.41%, more than a four-fold increase over that for cataract surgery alone (0.09%; P less than .05). The rates of endophthalmitis at 1 year were 0.58% and 0.13%, respectively, for cataract surgery with anterior vitrectomy and cataract surgery alone (P less than .0001). No significant differences in the rate of rehospitalization for endophthalmitis were observed based on the use of an intraocular lens, age, or race. Endophthalmitis within 1 year of surgery was 1.2 times more frequent in men than in women (0.16% vs 0.13%; P = .03). Overall, the likelihood of postoperative endophthalmitis from a national sample is consistent with case series previously reported.