Two brothers with butterfly-shaped macular dystrophy (BSMD) are reported. The anatomical and functional data were analyzed in 11 family members. Progressive photoreceptor dysfunction, supported by ERG abnormalities, was documented in both patients. The progression of the disease was observed over a period of seven years. The present observations emphasize that BSMD, at least in some cases, can be a chronic progressive disorder with secondary involvement of the photoreceptors.