Posterior Internal Ophthalmomyiasis (PIO) is the intraocular infestation by the fly larva of the order Dipterae. It is a rare clinical entity which prevalence is unknown. The disease may present with variable ophthalmological manifestations. The diagnosis of the disease is made by fundoscopic observation of typical findings and visualization of the fly larvae within the vitreous cavity. Treatment of ophthalmomyiasis includes observation, steroid administration, argon laser photocoagulation and surgical removal of the pathogen. In this report we present a case of PIO in which the initial symptoms included halo vision and diminished visual acuity in the right eye. Following the diagnosis, and due to lack of ophthalmological manifestations that could compromise ocular integrity, we opted for a conservative approach consisting only of periodic observation. This is the first case of PIO reported in the Mexican literature.