As a contribution to the study of complex structures in native Amazonian languages, this article examines the syntax of additives and conjunctions in the language of the Gavião of Rondônia. In this language the particle kĩĩ´í ‘also, too, and’ is used to form additive (‘also’) constructions with noun phrases and verb phrases, without creating conjoined syntactic constituents. The same particle is also used to form constructions with conjoined constituents, in which two or more verb phrases or two or more noun phrases are conjoined. The different functions of the particle have different and somewhat complicated syntactic structures. A brief description of basic Gavião syntax is provided, to have a basis for understanding the structure of the additives and conjunctions. Examples are given to describe the patterns observed and to provide tests to determine the constituent structure of the conjoined constructions. Composition rules for conjoined and additive constructions are offered when there is sufficient evidence. The semantic difference between participles and conjunctions is noted. Typological properties of Gavião additives and conjunction are discussed. Conjunction is of the postpositive bisyndetic type. Disjunction, ‘or’, which also appears in the language, is briefly described.