Objective: Fetal testosterone (fT) has organizational effects on the developing human nervous system and can be reliably estimated by the ratio between the length of the second and fourth digits -- 2D:4D. Previous studies reported altered patterns of fT in some developmental disabilities (e.g. ASD) relative to typically developing individuals (TD). Williams syndrome (WS) is a rare genetic disorder characterized by exacerbated empathy and social approach and heightened anxiety. Recent reports also highlight the co-occurrence of significant levels of autistic symptoms. Despite constituting an interesting model to study androgenic contributions to social behavior, no studies have sought to explore fT in WS. The main aims of this preliminary study were two-fold: (a) to compare 2D:4D in WS and TD; (b) to analyze the pattern of associations between 2D:4D and hypersociability, affective and cognitive empathy, anxiety and autistic symptoms in WS. Methods: 2D:4D were measured from digital scans of the ventral surface of the right hand. Hypersociability, empathy, anxiety and autistic symptoms were obtained from parental reports. Results: There were no significant differences in 2D:4D between WS than TD. In WS lower fT (higher 2D:4D) was significantly associated with hypersociability and affective empathy, as well as marginally associated with anxiety/depression scores. In contrast, cognitive empathy was marginally and negatively associated with 2D:4D, while levels of autistic symptoms were unrelated with this measure. Conclusion: Our results suggest that fT may be implicated in the emergence of several cardinal features of WS, namely hypersociability, affective empathy and anxiety, but not in ASD symptoms.