Purpose: To experimentally investigate knowledge of passives of actional ("hold") and psychological ("love") verbs in children with Williams syndrome (WS). Passives are usually reported to be in line with mental age in WS. However, studies usually focus on passives of actional verbs only. Method: Twenty-six children with WS, ages 6-16, and 3 groups of typically developing controls, ages 3;6-14;4 (years;months), individually matched to the WS group on nonverbal reasoning, receptive vocabulary, or grammar, participated. Their comprehension of actives and short and long passives (with and without the by-phrase) was tested using a sentence-picture-matching task. Results: Children with WS performed well above chance on passives of actional verbs but extremely poorly on passives of psychological verbs (short and long). Furthermore, their performance on both types of passives was worse than that of matched controls. Conclusions: The results reveal a previously unreported deficiency in the domain of syntax in WS, suggesting a particular difficulty with the structure of the verbal passive, not directly related to general levels of nonverbal abilities, receptive vocabulary, or general comprehension of grammar. It is argued that the difficulty in the formation of verbal passives in WS stems from a deficit in forming argument chains.