Purpose: To report successful therapy with gatifloxacin 0.3% ophthalmic solution (Zymar) in a patient with atypical mycobacterium keratitis after penetrating keratoplasty. Methods: A 58-year-old patient was referred for evaluation of microbial keratitis after penetrating keratoplasty. Results: Clinical examination of the patient revealed an infiltrate at the inferior graft-host junction with a satellite lesion with a mild inflammatory reaction in the anterior chamber. Microbiologic evaluation confirmed the diagnosis of atypical mycobacteria keratitis. The corneal abscess was completely eradicated with a topical course of gatifloxacin 0.3% with preservation of graft clarity and good visual acuity. Topical treatment with gatifloxacin 0.3% was continued for an additional period of 5 months. Conclusion: Topical gatifloxacin 0.3% may be successfully used to treat microbial keratitis resulting from atypical mycobacteria. © 2010 Lippincott Williams & Wilkins.