Abstract. Sharpening (a particular case of) a result of Szemerédi and Vu [SV06] and extending earlier results of Sárközy [S89] and ourselves [L97b], we find, subject to some technical restrictions, a sharp threshold for the number of integer sets needed for their sumset to contain a block of consecutive integers of length, comparable with the lengths of the set summands.A corollary of our main result is as follows. Let k, l 1 and n 3 be integers, and suppose that A 1 , . . . , A k ⊆ [0, l] are integer sets of size at least n, none of which is contained in an arithmetic progression with difference greater than 1. If k 2 ⌈(l − 1)/(n − 2)⌉, then the sumset A 1 +· · ·+A k contains a block of consecutive integers of length k(n − 1).