Background: Williams syndrome (WS), a neurodevelopmental disorder, is characterized by pervasive cognitive deficits alongside a relative sparing of auditory perception and cognition. A frequent characteristic of the phenotype is adverse reactions to, and/or fascination with, certain sounds. Previously published reports indicate that people with WS experience hyperacusis, yet careful examination reveals that the term "hyperacusis" has been used indiscriminately in the literature to describe quite different auditory abnormalities. Method: In an effort to clarify and document the incidence of auditory abnormalities in and among people with WS we collected data from parents of people with WS (n = 118) and comparison groups of people with Down syndrome, autism, and normal controls. Results: Our findings revealed four phenomenologically separate auditory abnormalities, all of which were significantly more prevalent in WS than the three comparison groups. Among people with WS, we found relatively few reports of true hyperacusis (lowered threshold for soft sounds) or auditory fascinations/fixations, whereas 80% reported fearfulness to idiosyncratically particular sounds, and 91% reported lowered uncomfortable loudness levels, or "odynacusis." Conclusions: Our results confirm anecdotal reports of an unusual auditory phenotype in WS, and provide an important foundation for understanding the nature of auditory experience and pathology in WS. We conclude by reviewing the ways in which the present findings extend and complement recent neuroanatomical and neurophysiological findings on auditory function in people with WS.