It is argued in this paper that equative sentences in Finnish Sign Language (FinSL) conform to the general schema of (NP) NP+(PI+)NP, parenthesis marking optionality of elements. With respect to this schema, it is further argued, (a) that the function of the first NP in equative sentences is always topic; (b) that topics are marked syntactically, prosodically, and morphologically in FinSL; (c) that the preferred organisation of equative sentences in general is topic-comment; (d) that there are two structurally distinct topic-comment structures in FinSL, one having the topic at the beginning of the clause and the other having the topic in the left-detached clause-external position; (e) that the double-indexing phenomenon (cf. pronoun copy) is functionally a means to increase textual cohesion; and (f) that the sign PI in equative sentences is a certainty expressing modal device, although it may be in the process of grammaticalising into a copula.