To describe the risk factors, management, and outcome of delayed Descemet membrane (DM) detachment after penetrating keratoplasty (PK) for keratoconus. We report 7 eyes from 6 cases and combine these data with 7 previous case reports identified by a search of PubMed. DM detachment occurred at a median of 25 years (range, 7-33 years) after PK. One individual had bilateral detachments. There was typically a mild ocular discomfort accompanied in some cases by a rapid onset of visual blur. Cases were often treated for allograft rejection before a DM detachment was suspected and confirmed by optical coherence tomography. Detachments were limited to the donor tissue in 11 eyes, but a DM break was identified at the time of onset in only 4 eyes. Thinning of the host corneal rim with ectasia was reported in 8 eyes (57%). In 3 eyes, the detachment resolved spontaneously, but in 2 eyes, a detachment was still present at 12 months. Gas tamponade to reattach the DM was performed in 9 eyes and was effective in 4 eyes. Five eyes underwent a repeat PK or endothelial keratoplasty. Histology showed fibroblastic proliferation on the stromal surface of the folded DM. The cause for DM detachment many years after PK is unknown, although progressive thinning of the host cornea and secondary graft ectasia may be implicated. Gas tamponade can be effective, but a repeat keratoplasty might be necessary. DM detachment should be included in the differential diagnosis for late-onset corneal edema after PK.