Six patients with masses located posterior to the bladder were biopsied using an anterior transcystic approach. Conventional biopsy needles were introduced through the bladder with both sonographic (five) and CT guidance (one). Clinically important diagnoses of recurrent carcinoma (four) or cytology-negative fluid (two) were made in all patients. One patient had a transient episode of minimal hematuria immediately after the biopsy. Otherwise, there were no complications. Transcystic biopsy appears to be a safe and effective technique for biopsy or aspiration of posterior pelvic masses.