Mastocytosis is a heterogeneous group of disorders in which mast cells exhibit clonal proliferation that infiltrates one or more organs. In cutaneous mastocytosis, the mast cells infiltrate the skin only, whereas systemic mastocytosis is diagnosed when at least one extra-cutaneous site is involved, with or without the skin being affected. Given the rarity of mastocytosis and the fact that skin rash can be a manifestation of different conditions and many clinicians are not familiar with this disorder, an accurate diagnosis may be delayed. We report a delayed diagnosis of indolent systemic mastocytosis in a 40-year-old gentleman who had been complaining of an unexplained skin rash for 6 years.