Retinitis pigmentosa (RP) is a group of retinal degenerative diseases that are characterised primarily by the loss of rod photoreceptor cells. Mutations in rhodopsin are the most common cause of autosomal-dominant RP (ADRP). Here, we propose a new classification for rhodopsin mutations based on their biochemical and cellular properties. Several different potential gain-of-function mechanisms for rhodopsin ADRP are described and discussed. Possible dominant-negative mechanisms, which affect the processing, translocation or degradation of wild-type rhodopsin, are also considered. Understanding the molecular and cellular consequences of rod-opsin mutations and the underlying disease mechanisms in ADRP are essential to develop future therapies for this class of retinal dystrophies.