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Introduction: Unilateral idiopathic condylar hyperplasia (UCH) is a condition that may cause malocclusion or facial asymmetry. Bone scintigraphy is important in planning of surgical treatment. It can assess the growing activity of the condyle. Conventional methodologies use the percentage difference between the activity of the two condyles or ratio of the condyle activity to a different bone reference area. W e verified the possibility of absolute quantification of activity with the new S iem ensxSPEC T Quant technology. Methods: SPECT/CT examination of the head after 99mTc-HDP administration was performed in 21 patients (8 men, 13 women, mean age 31.7 ± 11.9 years) with condyle hyperplasia. SUV values (average - SUVavg and maximum SUVmax) were obtained by modified iterative reconstruction OSCGM (Ordered Subset Conjugate Gradient Minimization). W e compared the SUV values in the regions of interest over the two condyles with conventional assessement represented by counting the ratio of activities from the summated transaxial slices. Significant asymmetry was defined as a 55 % or higher condylar uptake. Results: The difference between the ratio of SUVavg and the ratio of counts from the conventional technique was not significant (p = 0.1907). The differences were found for SUVmax (p = 0.01417), where significant proportional and systematic error were evident. The decreasing tendency of SUVmax with increasing age was apparent. The SUVmax values did not differ condyles with asymetrically higher activity from those ofthe rest of the population (p = 0.9654, p = 0.1654 for a relatively less active condyle respectively). Conclusions: The evaluation of growth activity in UCH is important in planning the optimal treatm ent approach. The ratio of SUVavg values from the new xSPECT-Quant system corresponds to the conventional methodology of semi-quantitative comparison of osteoblastic activity on SPECT, unlike the ratio based on SUVmax values. [ABSTRACT FROM AUTHOR]