The objective of the study was to assess phlebotomy loss in renal medical in-patients in order to minimise an iatrogenic cause of anaemia. Phlebotomy has been shown to be a significant cause of iatrogenic blood loss in critical care. However, there has been limited research in patients with renal disease, at risk from anaemia. A prospective observational study was conducted of 70 consecutive patients admitted to an acute renal medicine ward in a tertiary care hospital over a period of four months. Inclusion criteria included adult patients with acute or chronic renal failure. Patients actively bleeding were excluded. Blood loss due to phlebotomy was determined from the patient's computerised records. The mean patient age was 61.5 ± 16.5 years; the mean length of hospital stay was 23.1 ± 19.8 days. The mean admission Hb was 9.8 ± 2.0 g dL−1 and 9.5 ± 1.5 g dL−1 on discharge. The total mean blood loss from phlebotomy during hospitalisation was 215.8 ± 166 mL with a mean weekly blood loss of 55.7 ± 11.23 mL. Losses were highest in the first week (mean of 76.8 mL), declining in subsequent weeks. Samples were taken for biochemistry (38%), FBC (36%), transfusion (13%) and others (13%). 46% of patients were transfused (mean 4.8 ± 3.6 units). Blood loss was lower than in previous studies conducted in intensive care and general medicine but clinical staff should be aware of the cumulative blood loss from phlebotomy. Losses should be managed by optimising the frequency and volume of blood drawn for diagnostic laboratory tests.