Objective This study assessed the quantitative evaluation of the region of interest (ROI) by mean and maximum pixel counts of single-photon emission computed tomography (SPECT) scans in patients with clinical suspicion of unilateral condylar hyperactivity (UCH); the interobserver reliability and the correlation of condylar activity with patient age was determined. Methods Two independent observers analyzed 67 bone SPECT scans. Maximum and mean activity values within an ROI on the mandibular condyle were analyzed; a cutoff value of 55% was used to determine the qualitative outcome. Results Excellent interobserver agreement was seen for both maximum (kappa 1.0) and mean activity analysis (kappa 0.94). Maximum and mean condylar activities were strongly correlated ( r > 0.98). Maximum and mean condylar activity of the normal condyle decreased significantly with increasing age. Conclusions Maximum and mean condylar activity levels were highly correlated in patients with mandibular asymmetry. An excellent interobserver agreement was found with either maximum or mean condylar activity.