Isaiah 57,3-13 appears to be a harsh polemic against some of the cults of the postexilic community in Jerusalem. The poem presents however many difficulties, so that the real nature of the cults as well as the precise meaning and intention of the text remain somewhat obscure. This paper will first (1.) address the problem of the origin of the poem, and will locate it within the growth of the body of material know as « Third Isaiah » (Isa 56-66); a dating in the second half of the fifth century B.C. is suggested. Then (2.), it is proposed to read the text of Isa 57,3-13 as a condemnation of three different cults, identified as follows: fertility cult (v. 5a, echoed in vv. 7-8), child sacrifice (cult of Molech: VV. 5b // 9a), and cult of the dead (vv. 6 // 9b). It is further argued that these cults still played an important part in « popular religion » in Persian Yehud during the fifth century. The question remains, however, as to why these three cults are so closely linked in our poem. In a final section (3.), it is argued that what these cults have in common is to belong to the sphere of the family (reproduction, children, dead ancestors), and that the text, read together with 56,1-8, should be seen as a criticism of the weight of lineage and kinship in the cultic community of fifth-century Jerusalem.