P-bodies are cytoplasmic foci that are sites of mRNA degradation and translational repression. It is not known what causes the accumulation of RNA-degradation factors in P-bodies, although RNA is required. The yeast Lsm1-7p complex (comprising Lsm1p to Lsm7p) is recruited to P-bodies under certain stress conditions. It is required for efficient decapping and degradation of mRNAs, but not for the assembly of P-bodies. Here we show that the Lsm4p subunit and its asparagine-rich C-terminus are prone to aggregation, and that this tendency to aggregate promotes efficient accumulation of Lsm1-7p in P-bodies. The presence of glutamine- and/or asparagine-rich (Q/N-rich) regions in other P-body components suggests a more general role for aggregation-prone residues in P-body localization and assembly. This is supported by reduced P-body accumulation of Ccr4p, Pop2p and Dhh1p after deletion of these domains, and by the observed aggregation of the Q/N-rich region from Ccr4p.