Malattia Leventinese (ML) is an autosomal dominant inherited macular degeneration with a middle-age onset. Phenotypically, the disease closely resembles Age-related Macular Degeneration (AMD), a condition affecting 20% of the population over age 65 and the leading cause of blindness in the elderly in the Western world. Patients with ML suffer from decreased visual acuity and have a characteristic radial pattern of deposits, called drusen, which form beneath the retinal pigment epithelium (RPE). A single missense mutation (R345W) in the Epidermal Growth Factor Containing Fibrillin-like Extracellular Matrix Protein 1 (EFEMP1) gene is responsible for the disease, and leads to the misfolding and inefficient secretion of the protein. In normal retinas, the protein localizes to the inner photoreceptor matrix (IPM), apical to the RPE, while in individuals with ML, it resides between the RPE and drusen. We therefore surmised that wild-type EFEMP1 is apically secreted by the RPE, and that the R345W mutation misdirects this secretion basolaterally. To test this hypothesis, we utilized a cell culture system consisting of polarized monolayers of human fetal RPE (hfRPE) cells grown on Transwell membranes. AAV2/1 vectors containing FLAG-tagged wild-type or mutant EFEMP1 were used to transduce the hfRPE cells with high efficiency. Transduction did not affect hfRPE cell polarization or tight junction formation, as shown by immunofluorescence staining for Na+/K+ ATPase, CD147, and ZO-1. Immunoprecipitation of EFEMP1-FLAG from the basolateral and apical medium revealed that, contrary to our hypothesis, EFEMP1 is secreted basolaterally, and that this polarized secretion pattern is not altered by the R345W mutation. In addition, we found that this pattern of secretion was distinct from dog epithelial (MDCK) cells, which secreted the protein apically. Additional immunoprecipitation and immunofluorescence experiments indicated that the R345W mutation resulted in retention of EFEMP1 within polarized RPE cells. We conclude that EFEMP1 is directionally secreted from epithelial cells, and that its basolateral secretion from RPE cells may be indicative of some yet unknown function in the extracellular matrix underlying those cells, within the local environment of drusen formation in ML patients. However, the absence of an alteration in polarized secretion suggests that the intracellular retention of mutant EFEMP1 may be a major contributing factor to the progression of ML.