AIMS/HYPOTHESIS: We investigated the relationship between haemoglobin (Hb) and diabetes in patients with renal disease. SUBJECTS, MATERIALS AND METHODS: All adult patients with stable chronic kidney disease attending renal or diabetic outpatient clinics in a six-month period were identified. Patients' notes and electronic patient records were used to build a comprehensive biochemical and clinical database. Results were analysed for the predictors of Hb, the severity of anaemia in both groups and the relative impact of diabetes on haemoglobin and anaemia. RESULTS: The study group consisted of 468 patients, of whom 204 had diabetes and 264 did not. At every level of renal function haemoglobin levels were lower by an average of 10 g/l in subjects with diabetes than in those without. Likewise, anaemia was found to occur at an earlier stage of chronic kidney disease (and to be of greater severity) in diabetic patients. Independent predictors of haemoglobin included female sex, diabetes, renal function and serum albumin, with diabetes and renal function being the greatest predictors. Multiple logistic regression showed that patients with diabetes had an odds ratio of 4 for being anaemic. Had we used an estimated GFR of less than 60 ml/min to trigger investigation of anaemia, we would have detected 85% of anaemic patients. CONCLUSIONS/INTERPRETATION: Anaemia is frequently found in diabetic patients with renal disease, occurs earlier and is more severe than in similar but non-diabetic subjects. In contrast to previous publications, our findings suggest that anaemia is prevalent at the earliest stages of chronic kidney disease. We advocate an estimated GFR threshold of <60 ml/min to trigger investigation for anaemia in diabetic subjects.