The current study examined the acquisition of relative clauses (RCs) in Persian-speaking children. Persian is a relatively unique data point in crosslinguistic research in acquisition because it is a head-final language with post-nominal RCs. Children (N = 51) aged 2 to 7 years completed a picture-selection task that tested their comprehension of subject-, object-, and genitive-RCs. The results showed that the children experienced greater difficulty processing object and genitive RCs when compared to subject RCs, suggesting that the children have particular difficulty processing sentences with non-canonical word order. The results are discussed with reference to a number of theoretical accounts proposed to account for sentence difficulty.