Despite a widespread belief that private insurers spend large amounts on health care for enrollees receiving dialysis, data limitations over the past decade have precluded a comprehensive analysis of the topic. To examine the amount and types of increases in health care spending for privately insured patients associated with initiating dialysis care. A cohort study covering calendar years 2012 to 2019 included patients with kidney failure who had employer-sponsored insurance for 12 months following dialysis initiation. Data analysis was performed from August 27, 2021, to August 18, 2022. The data cover the entirety of the US and were obtained from the Health Care Cost Institute. The data include all medical claims for enrollees in employer-sponsored health insurance plans offered by multiple major health care insurers within the US. Participants included patients younger than 65 years who were continuously enrolled in these plans in the 12 months before and after their first claim for dialysis care. Patients also had to have nonmissing documented key characteristics, such as sex, race and ethnicity, and health characteristics. A claim for dialysis care. Out-of-pocket, inpatient, outpatient, physician services, prescription medication, and total health care spending. The hypothesis tested was formulated before data collection. The sample included 309 800 enrollee-months, which was a balanced panel of 25 months for 12 392 enrollees. At baseline, 7534 patients (61%) were male, 5415 (44%) were aged 55 to 64 years, and patients had been enrolled with their insurer for a mean of 30 months (95% CI, 29.9-30.1 months). In the 12 months before initiating dialysis care, total monthly health care spending was $5025 per patient per month (95% CI, $4945-$5106). Dialysis care initiation was associated with an increase in total monthly spending of $14 685 (95% CI, $14 413-$14 957). This increase occurred across all spending categories (dialysis, nondialysis outpatient, inpatient, physician services, and prescription drugs). Monthly patient out-of-pocket spending increased by $170 (95% CI, $162-$178). These spending increases occurred abruptly, beginning about 2 months before dialysis initiation, and remained increased for the subsequent 12 months. In this cohort study, evidence that private insurers experience significant, sustained increases in spending when patients initiated dialysis was noted. The findings suggest that proposed policies aimed at limiting the amount dialysis facilities charge private insurers and the enrollees has the potential to reduce health care spending in this high-cost population.