Phagocytosis and elimination of shed aged photoreceptor outer segments (POS) by retinal pigment epithelial cells is crucial for photoreceptor function and survival. Genetic studies on a natural animal model of recessive retinal degeneration allowed the identification of MerTK, the gene encoding the surface receptor required for POS internalization. Following this discovery, screenings of DNA samples from patients have revealed that MERTK mutations cause retinal degenerations in humans. MERTK patients present some of the classical symptoms of retinitis pigmentosa, but it is atypical in that the disease develops very early during childhood and the macula is also involved early on. Therefore, the phenotype ought to be qualified as a rod-cone dystrophy. Recently, MERTK has been implicated in various types of cancers and sclerosis. This review identifies the different MERTK mutations known so far and describes associated pathologies.