We report on 134 fine needle biopsies in 127 patients with an ultrasound finding suggesting renal malignancy. Biopsy was performed guided by dynamic ultrasound using an 0.6 mm aspiration needle for cytology and an 0.8 mm Surecut needle for histology. The retrieval rate for cytology was 97.8% compared to 79.1% for histology. Sensitivity for cytology and histology was 89.4% and 70.6%, respectively. The specificity of cytology was 85.4% giving a predictive value of a positive result of 91.6%. Specificity and positive predictive value for histology were both 100%. We conclude that fine needle aspiration biopsy from renal masses in our hands carries too high a false positive rate to be clinically safe. We recommend that fine needle histological biopsy replaces the aspiration biopsy in case of renal masses.