Purpose: Multiple factors impact reading acquisition in individuals with reading disability, including genetic disorders such as Williams syndrome (WS). Despite a relative strength in oral language, individuals with WS usually have an intellectual disability and tend to display deficits in areas associated with reading. There is substantial variability in their reading skills. While some authors have postulated that phonological deficits are at the source of their reading deficits, others have suggested that they can be attributed to visuospatial deficits. This study was the first to undertake an in-depth exploration of reading skills among French-speaking children and adults with WS. We tested the assumption that some factors influence performance on single-word identification among individuals with WS, with a focus on the roles of phonological awareness and visuospatial skills. Method: Participants were 29 French-speaking adults with WS and 192 controls matched for nonverbal mental age and reading level. We administered tests assessing reading (decoding and word recognition), vocabulary (expressive and receptive), and phonological and visuospatial skills. We also controlled for chronological age and nonverbal reasoning. Results: Phonemic awareness was the most predictive factor of single-word identification in the WS group. Visuospatial skills also contributed, but not more or beyond other factors. More broadly, reasoning skills may also have accounted for the variability in single-word identification in WS, but this was not the case for either chronological age or vocabulary. Conclusions: There is considerable heterogeneity among adults with WS, who may be either readers or prereaders. Similar profiles identified among individuals with other specific learning disabilities suggest that high reading variability is not specific to the neuropsychological profile of WS. We discuss a multidimensional approach to the factors involved in reading deficits in WS.