To analyze the reasons for intraoperative perforation of Descemet's membrane during deep anterior lamellar keratoplasty (DALK) during the learning curve. DALK was attempted in 35 eyes of 33 patients with pathologies involving the corneal stroma and sparing of Descemet's membrane (DM), including patients with keratoconus, corneal stromal dystrophies and healed keratitis. The surgical plan included complete removal of the corneal stroma using the "big bubble" technique for exposing Descemet's membrane followed by grafting of a full-thickness corneal stromal lenticule. DALK was converted into full-thickness penetrating keratoplasty in eight eyes (23%), which included patients with keratoconus (n = 6), macular corneal dystrophy (n = 1) and healed keratitis (n = 1). Main reasons for conversion were perforation of the DM due to excessive air injection (four eyes) and improper surgical maneuvers (three eyes). One case had deposits on Descemet's membrane upon exposure of the DM. A successful penetrating keratoplasty could be performed in all eight eyes. During the learning curve, excessive air injection and inappropriate surgical maneuvers may complicate a DALK resulting in conversion to penetrating keratoplasty.