Aim and objective: To report a case of a patient with Down syndrome (DS) and keratoconus who experienced acute hydrops in one eye as well as sterile perforation requiring emergent tectonic penetrating keratoplasty following epithelium-off corneal collagen cross-linking (CXL) in the fellow eye. Background: Keratoconus is a progressive, bilateral, corneal ectasia in which there is stromal thinning and apical protrusion of the cornea resulting in irregular astigmatism. This condition has been shown to have a disproportionately high association with DS. We describe a unique case that highlights this potentially rapidly progressive disease and its manifestations. Case description: An 18-year-old male with history of DS presented with bilateral floppy eyelid syndrome and corneal ectasia as well as acute hydrops of the right eye (OD). Medical management included 5% sodium chloride drops, prophylactic antibiotic ointment, and counseling against eye rubbing and to wear a Fox shield when sleeping. Worsening hydrops OD prompted intracameral injection of 20% SF₆ gas which hastened resolution of edema within 3 weeks. Residual severe corneal scarring, however, limited visual improvement to light perception. Meanwhile, progressive ectasia of the left eye (OS) prompted epithelium-off CXL procedure. Sterile corneal perforation was noted 4 days following uneventful surgery, necessitating emergency tectonic penetrating keratoplasty and temporary tarsorrhaphy. Conclusion: This case illustrates that patients with DS and keratoconus are at especially high risk for rapidly progressive disease and for surgery-related complications. Clinical significance: Patients with keratoconus, especially younger patients that can experience rapid progression, need to be closely monitored with early intervention but can still experience uncommon complications. Similar at-risk patients may be considered instead for investigational non-FDA-approved epithelium-on cross-linking, which should intuitively be associated with a lower risk of corneal perforation.