In advanced chronic kidney disease (CKD), patients with obesity often have better outcomes than patients without obesity, often called the ‘obesity paradox’. Yet, in CKD, the prevalence of inflammation increases as CKD progresses. Although a potential confounder, inflammation may be left unaccounted in obesity–mortality studies. We examined the associations of body mass index (BMI) with all-cause and cause-specific mortality across CKD stages, with consideration for uncontrolled confounding due to unmeasured inflammation.