Loss of renal function is associated with inflammation and immune system impairment, which results in an increased susceptibility to viral and bacterial infections, poor vaccination responses and an increased risk of malignancies in patients with end-stage renal disease (ESRD). Here, Michiel Betjes describes the effects of uraemia and renal transplantation on cells of the adaptive and innate immune systems. He also outlines the clinical implications of immune system impairment in patients with ESRD and discusses the concept of premature immunological ageing in these patients.