Background Orbital cellulitis is a vision-threatening emergency. Distinguishing it from preseptal cellulitis can be difficult on initial presentation. Method We describe the case of a paediatric patient with permanent unilateral vision loss from progressive orbital cellulitis. Earlier diagnosis and surgical management may have saved this patient's vision. Case A seven year-old with no past medical history was transferred to our hospital with worsening right eye swelling, after 3 days of IV antibiotics at a peripheral hospital. She was systemically unwell with fevers, lethargy and anorexia. Her right eye was swollen shut with profound chemosis and facial cellulitis extending bilaterally. There was significant proptosis and increased orbital retropulsion. CT showed severe orbital cellulitis, medial subperiosteal abscess, extra-conal collections in the orbit with multiple gas locules, and features of acute sinusitis. The anterior ethmoid and maxillary sinuses were drained endoscopically and the laminal papyracea partially removed. The orbital abscesses were drained via a subcilliary incision extended into the lateral canthus. Operative cultures grew Eikenella corrodens, Prevotella spp. and Haemophilus influenza and antibiotics were rationalised to ceftriaxone. The patient's visual acuity corrected to 6/9 in the affected eye, but there was severely restricted visual field. Conclusion Preseptal cellulitis should be treated as a precursor of orbital cellulitis, especially in the setting of intercurrent URTI or sinusitis. Orbital cellulitis may progress rapidly so early assessment by ENT and Ophthalmology teams is essential. Urgent CT is indicated in the presence of visual/neurologic compromise, when visual assessment is not possible, or the patient fails to improve after 24 hours of therapy.