A series of 121 consecutive patients with abdominal (96 cases) and retroperitoneal (25 cases) masses was studied in order to evaluate the contribution of cytology in establishing a definite diagnosis of the tumors. The cytologic results on aspirates were obtained with 22 or 23 gauge Chiba needles. At the same time, percutaneous fine needle aspiration biopsy was performed with 19 or 21 gauge fine needles having circumferentially bevelled tips that produced tiny tissue cores suitable for histologic study in 88 cases. These diagnoses were controlled with larger pathological specimens in 78 cases and appeared to be consistent with the clinical and biological course in 43 cases. The sensitivity of the cytologic diagnosis was 83 per cent, and its overall accuracy 87.6 per cent. There were no false-positive results. Furthermore, the method proved to be safe and well-tolerated, with low morbidity (0.8 per cent) and no mortality.