A revision of Rhododendron subgenus Tsutsusi is presented: section Tsutsusi with 66 species is equivalent to series Azalea subser. Obtusum; and section Brachycalyx with 15 species includes some species previously placed in subser Schlippenbachii. One new species in section Tsutsusi, R. arunachalense Chamberlain & Rae, sp. nov., is described. Distribution maps are provided for most of the species.