This work discusses aspects of linguistic variation in particularly complex relative clauses, with a special focus on European Portuguese. Two groups of relative clauses are focussed, resorting to data from electronic corpora, mainly containing newspaper texts: clauses headed by the phrase «em relação a» 'in relation to', and similar forms, when associated with a topic value; clauses with the (variable) pronoun «cujo» 'whose', which prototypically illustrate the relativization of genitive complements. Intriguing relations between the two groups of clauses are also shown, which are manifest in structures where a genitive complement is associated with a topic value. Overall, this paper illustrates how, in highly complex syntactic constructions, variation – involving competition among equivalent forms – and grammatical anomaly – involving various degrees of rejection of utterances (by groups of speakers of a given variety) – play a pivotal role in the dynamics of linguistic change.