We studied prospectively 32 consecutive patients with new onset of gross or microscopic hematuria while on anticoagulant therapy. Of the patients 19 men and 11 women (mean age 65 years) underwent urological evaluation. Of 6 patients with microscopic hematuria 3 with nephrolithiasis subsequently underwent extracorporeal shock wave lithotripsy. Two of 24 patients (7%) with gross hematuria had neoplastic disease invading the bladder, 1 had benign prostatic hyperplasia requiring resection, 1 had urethral stricture, 1 had ureteropelvic junction obstruction and 1 had nephrolithiasis. Thus, significant urinary tract disease was present in 9 patients (30%). Hematuria resolved in more than 90% of the patients after treatment. Based upon these observations, we believe that gross or microscopic anticoagulant associated hematuria is frequently precipitated by a significant genitourinary pathological condition and its prompt evaluation is recommended.