A statistical analysis of the accuracy of the immediate interpretation of 425 fine needle aspiration (FNA) biopsies from various sites was performed. Preliminary interpretation of Diff-Quik-stained smears was rendered within a few minutes after performing the FNA biopsy, using diagnostic terminology similar to that of a surgical pathology report. The immediate assessment was documented in the formal cytology report and compared to the final diagnosis. For the entire series, the immediate interpretation had a sensitivity of 96%, a specificity of 97%, a positive predictive value (PV) of 98%, a negative PV of 95% and an efficiency of the test of 96%. There were 14 false-negative or falsely insufficient immediate interpretations and one false-positive immediate diagnosis. The diagnostic accuracy of the immediate interpretation of FNA biopsies from specific sites was also calculated; FNA biopsies of the pancreas were the least accurate procedure, having a sensitivity of 60% but a specificity of 100%. The role of the immediate interpretation of FNA biopsies is similar to the use of frozen sections in surgical pathology. An immediate assessment can (1) determine whether an adequate specimen is present, (2) render a specific preliminary diagnosis, (3) guide further clinical investigations or treatment, and (4) determine whether ancillary studies are needed to make a more accurate or specific diagnosis from the FNA specimen. Our results indicate that the immediate interpretation of FNA biopsies is an accurate procedure that should be routinely employed.