Many chemotherapeutic agents are nephrotoxic and/or excreted via the kidney. Thus, careful evaluation of renal function is important since drug dosages are often lowered in patients with impaired renal function. When the creatinine clearance as calculated by the method of Cockcroft and Gault from the patient's age, weight, and serum creatinine was compared to the measured creatinine clearance in the same patients, the correlation coefficient was low (r = 0.40) and the average difference between the predicted and measured creatinine clearance values was 25.3%. Thus, in our patient population, creatinine clearance calculated by the method of Cockcroft and Gault did not correlate well with measured creatinine clearance and thus was not useful as a clinical tool.