This is the first reported case of delayed-onset postcataract endophthalmitis caused by Mycobacterium goodii, confirmed by multiple cultures. The patient had uneventful cataract removal by phacoemulsification with implantation of a posterior chamber intraocular lens (IOL). One month later, he developed redness, pain, a hypopyon, and a decrease in visual acuity to finger counting in the affected eye. A vitreous biopsy was performed for suspected endophthalmitis; culture results showed rapidly growing bacteria identified by DNA sequencing as Mycobacterium goodii. The eye ultimately required IOL explantation but had a good final outcome with 20/40 uncorrected vision. Mycobacterium goodii is a rapidly growing Mycobacterium with isolates more commonly occurring in cellulitis, osteomyelitis, and respiratory disease. Single-drug antibiotic therapy for nonocular disease is often sufficient if the correct antimicrobial agent is used. The newer fluoroquinolones are promising against rapidly growing Mycobacterium.