Objectives To characterise the risk factors for chronic idiopathic normocytic anaemia (CINA) in older people, particularly the role of age-associated renal impairment. Methods Patients aged >= 65 years admitted to a medical unit over 12 months were assessed. Those with secondary causes of anaemia including chronic kidney disease (CKD) were excluded. CINA was defined as a haemoglobin <130 g/l for men and <120 g/l for women for at least 6 months without any apparent cause. Renal function was determined by estimating creatinine clearance (CrCl) using Cockcroft-Gault formula, and glomerular filtration rate (GFR) using modification of diet in renal disease (MDRD) and chronic kidney disease epidemiology collaboration (CKD-EPI) formulas. Results 116 had CINA. Controls were 572. The mean estimates of renal function were significantly lower in cases as compared with controls (P < 0.001). The risk of CINA increased by 12.6, 10.4 and 12 %, respectively, for each unit decrease in CrCl, MDRD-eGFR and CKD-EPI-eGFR, independent of age and other covariates. The adjusted odds ratios for CINA in those with CrCl, MDRD or CKD-EPI eGFR <60 ml/min/1.73 m(2) were 2.68 (CI 1.53-4.70); 2.70 (CI 1.57-4.62) and 2.12 (CI 1.46-3.74), respectively. Other covariates in the model that were independently associated with CINA included advanced age, diabetes mellitus (DM), use of angiotensin converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB), history of dementia and living in a residential care facility. Conclusions Age-associated renal impairment independently contributes to CINA. Other potential risk factors for CINA include advanced age, DM and ACEI or ARB use.