Structural synonymy is exhibited by sets of expressions that are capable of conveying the same denotative content but are differently constructed and hence have slightly different meanings. Synonymous structures, due to the general complexity of syntactic phenomena, are not quite coterminous semantically, stylistically, or pragmatically; hence, they are not synonyms in the strict sense. It is exactly such differences that make it possible for them to offer a choice for the language user. Formal variants, in the author's view, are sets of syntactic structures that do not exhibit any semantic diversity despite their formal differences; hence, they are freely interchangeable (or, in the case of historical phenomena, are assumed to be such on the basis of available data). The existence of formal variants is the basis of the subsequent emergence of synonymous constructions. This paper discusses variation and structural synonymy in one type of complex sentences: those involving relative clauses. The data are taken from parallel passages of six different Hungarian translations of the Bible written between 1416 and 1626, supplemented by two contemporary translations of the same passages.