The purpose of this study was to examine the quantitative changes in subperiosteal empyema (SE) size over time and the time to complete radiographic resolution of this. This was a retrospective case review of 15 cases with orbital cellulitis and SE with repeat imaging without surgery. Location was medial in 13/15 cases, one superior and one superior-medial. Mean size for transverse, anterior-posterior, cranial-caudal axes were 4.7±3.1, 16.7±9.9 and 9.7±4.4mm respectively. On follow-up measurements were 4.1±3.9, 10.2±8.4 and 6.4±4.7mm respectively. Mean volume was 3.1±2.3cm3 reducing to 1.9±1.9cm3 at follow-up. On average size increased in the first two to three days and then reduced over two to three weeks. All were treated medically. Two needed surgery with clinical deterioration. The authors propose the natural radiographic course of medically managed SE should aid management decision-making in these cases.