The current study investigated the development of figurative language production, including different types of figurative expressions, during a fictional narrative in 20 typically developing (TD) children and 20 children with Williams syndrome (WS) aged 7-18 years old. In contrast to previous studies, developmental trajectories showed that (1) the production of figurative expressions in TD children did not change with age, (2) the WS group produced a similar amount of figurative expressions in comparison to the TD group, (3) but regression analyses showed that, out of a number of verbal and non-verbal standardised background measures, synonymy knowledge was the best predictor for figurative language production scores in WS. Both the clinical and theoretical implications of these results are discussed. (Contains 1 figure and 2 tables.)