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.