To define normal limits for serum creatinine levels, as well as to explore the relationship between age and the prevalence and severity of renal disease in patients with sickle cell anemia (SCA), we retrospectively analyzed renal function parameters in 368 patients followed in our SCA clinic. Dipstick proteinuria was present in 78 patients (20.6%). Chronic renal insufficiency (CRI) was present in 17 patients (4.6%) and showed a high degree of association with proteinuria and increased age. In patients with CRI, the severity of renal dysfunction was also age-related. In the 284 patients without proteinuria or CRI, mean serum creatinine levels were lower than predicted. We conclude that in patients with SCA, serum creatinine levels at the upper limit of normal should be regarded with suspicion, and that the prevalence and severity of proteinuria and CRI in SCA is high and increases with age.