PURPOSE: Acute hydrops develops when Descemet's membrane and the endothelium of the ectatic cornea separates to allow aqueous humor to enter the stroma. The current study was done to determine if penetrating keratoplasty (PK) in keratoconus patients with resolved hydrops has a poor prognosis. METHODS: A retrospective chart review of 35 eyes of 35 patients with keratoconus who underwent PK after the resolution of acute hydrops (Group 1) and of 74 eyes of 69 patients who had PK without a previous history of acute hydrops (Group 2) was performed. The chi-square test was used for statistical analysis. RESULTS: The mean age in Group 1 was 21.1±11.0 years. The mean age in Group 2 was 23.2±14.4 years. Vernal keratoconjunctivitis was present in 11 patients in Group 1 (31%) and in 12 (17.4%) patients in Group 2. Loose sutures were present in two patients (6%) in Group 1; both resulted in loose suture-related corneal neovascularization. Loose sutures developed in five patients (7%) in Group 2. In Group 1, three patients (9%) had microbial keratitis. Microbial keratitis was seen in five patients (7%) in Group 2. Two patients (6%) in Group 1 developed late endothelial graft failure. In Group 2, one eye (1%) developed early and one eye (1%) late epithelial graft rejection; five eyes (7%) developed late endothelial graft rejection. There was no statistically significant difference between the two groups with respect to the incidence of graft rejection. At the last examination, 34 eyes in Group 1 had clear grafts; in the second group, graft clarity was achieved in 71 eyes. CONCLUSION: Penetrating keratoplasty in hydrops is successful in terms of graft clarity and visual outcome in patients with keratoconus after the resolution of hydrops. The patients should have preoperative and postoperative anti-allergic treatment and close follow-up for possible complications.