Four hundred thirty-six patients with carcinoma of the prostate had lymphangiography (LAG) as part of their initial evaluation before treatment. Fine-needle aspiration biopsy (FNAB) of abnormal opacified lymph nodes was performed routinely. The positivity rate of LAG and FNAB in each clinical stage was compared with the positivity rate predicted for that stage, based on published series of patients with carcinoma of the prostate who underwent pelvic lymph node dissection (LND). Within each clinical stage, the relation of the outcome of LAG/FNAB to histologic tumor grade (Gleason score) and serum acid phosphatase levels was evaluated. LAG/FNAB was of very limited value in patients with less than clinical stage C disease and of no value in patients with a Gleason score of less than 6. Although LAG/FNAB is insensitive even in clinical stage C disease, a positive result will avoid the morbidity and expense of a staging LND and allow confident selection of appropriate treatment. A negative LAG/FNAB, on the other hand, is meaningless, because of the high false-negative rate of LAG. Since no two study populations are exactly alike, any evaluation or comparison of tests used to stage patients with carcinoma of the prostate should state the distribution of its patients by clinical stage.