During fieldwork carried out in January‐February 1995 in the Strict Nature Reserve No. 9 ≪Tsingy de Bemaraha≫ (western Madagascar), a new species of dwarf chameleon (genusBrookesia)was discovered on the western slopes of the Antsingy forest. The inaccessible habitat of this new taxon consists of dense subhumid tropophile forest growing among the limestone blocks belonging to the huge karstic complex of the ≪Tsingy de Bemaraha≫ Massif, whereBrookesia exarmatasp. nov. is sympatric withBrookesia perar‐mata, a taxon likely endemic to the Antsingy forest, andBrookesia brygooi. The new taxon, formally described in this paper, is a small‐sized chameleon whose total adult length ranges between 30 and 45 millimetres: this feature, together with the absence of a pelvic shield and the presence of a series of dorsolateral tubercles (or a few small dorsolateral spines), leads toBrookesia exarmatabeing ascribed to theBrookesia minimagroup.Brookesia tuberculataandBrookesia peyrierasiare ressurrected from the synonymy ofBrookesia minimaand a new identification key to these and to the other three species included in theBrookesia minimagroup is proposed.