In the evaluation of soft tissue tumors primary sarcomas must be differentiated from other malignancies, such as cancer metastases, malignant lymphomas, as well as benign tumors and tumor-like conditions. As far as possible this should be done without open biopsy to avoid local spread. Fine needle aspiration biopsy as opposed to thick needle biopsy utilizes smaller needle diameters up to 0.8 mm with assumed negligible risks of local or distant tumor spread. Such a fine needle aspiration biopsy for cytodiagnosis was supposed to increase the reliability of the preoperative diagnosis. In a consecutive series of 187 patients referred to an orthopedic oncology group because of suspected malignancy fine needle aspiration biopsy was made. In 129 cases with histology and in 49 non-operated cases with at least 2 years of clinical follow-up the reliability of the method is analyzed. In 163 cases the aspirated material was sufficient for a diagnosis and 152 cytological reports were correct regarding the diagnosis of a malignancy contra a benign tumor or tumor-like condition. Thirty-five of 43 malignancies were primary soft tissue sarcomas, 28 of these with a correct cytologic diagnosis of sarcoma. Eight were malignant lymphomas or carcinomas. Fourty-nine patients with 48 benign and one malignant cytological diagnosis were not operated upon. At least 2 years of clinical follow-up confirmed a benign diagnosis in these cases. The total reliability is thus around 85%. Fine needle aspiration biopsy is considered to be a very valuable complement to other investigations in the diagnostic work-up of soft tissue tumors.