Several recently published reports have advanced our understanding of the epidemiology of anemia associated with chronic renal insufficiency. Anemia is commonly observed among subjects with chronic renal insufficiency. In comparison with subjects with preserved renal function, a significant decrease in hemoglobin could be detected in subjects with more modest degrees of renal insufficiency than was previously realized. Some of this undoubtedly reflects a decrease in renal production of erythropoietin, but these subjects may also suffer concomitant 'anemia of chronic disease'. Anemia is more likely not only among those with worse renal insufficiency, but also among black subjects, those with relative iron deficiency and those with lower serum albumin. Compared with those with preserved renal function, a significant decrease in hemoglobin could be detected in men at higher estimated creatinine clearance levels than in women; and at any given creatinine clearance, the decrease in hemoglobin is greater in men than in women. In the US, 800000 adults were estimated to suffer chronic renal insufficiency associated anemia, defined as hemoglobin level below 11 g/dl. As detailed in the present review, several methodological issues should be kept in mind when interpreting the literature. Further studies are needed to define the clinical implications of this common condition and to determine the most appropriate therapeutic response.