© Science Printers and Publishers, Inc.OBJECTIVE: To determine whether nuclear morphometric analysis could be used as an additional tool to determine the malignancy risk in cases of atypia of undetermined significance / follicular lesion of undetermined significance, thereby helping to prevent unnecessary surgery in this group of patients. STUDY DESIGN: Nuclear morphometric study was performed on the cytological specimens of 45 patients who had undergone thyroid surgery. Ten parameters were studied: perimeter, feret minimum, feret maximum, nuclear area, shape factor, form factor, roundness, diameter, nuclear size, and coefficient of variation of the nuclear area. RESULTS: All of the studied morphometric parameters, excluding only the form factor, were lower in the nonneoplastic lesion group as compared to those of the neoplastic lesion group. Statistically significant differences were evident for nuclear area (66.11±18.54 μm2 vs. 79.64±17.86 μm2, respectively, p=0.019), nuclear size (9.41±1.26 μm2 vs. 10.17±1.16 μm2, respectively, p=0.048), perimeter (32.38±4.57 μm vs. 35.1± 3.97 μm, respectively, p=0.047), and feret maximum (11.27± 1.58 μm vs. 12.24±1.54 μm, respectively, p=0.049). CONCLUSION: Certain nuclear morphometry parameters, such as perimeter, feret maximum, nuclear area, and nuclear size, could be used to determine malignancy risk. Both nuclear area and nuclear size measurements demonstrated a higher sensitivity with a higher negative predictive value, while nuclear size measurement had the highest diagnostic accuracy.