INTRODUCTION: Prader-Willi syndrome (PWS) is a rare genetic condition associated with global intellectual impairment. While research has evidenced speech problems, little is known about reading, which is a critical language ability involved in communication. The aim of the present study was to investigate vocabulary and reading skills in adults with PWS. METHOD: A total of 56 individuals (35 females, mean age = 33.64 years, range = 19-57 years) with PWS participated. Standardized paper and pencil tests were used to examine the level of vocabulary (LexTale-FR test) and reading performance (Alouette-R test). Two computerized tasks were also administered to assess the efficiency of lexical and phonological processes in reading (lexical and phonological decision tasks, taken from the ECCLA software). Performance was analyzed and compared with available norms on neurotypical adults and/or children. RESULTS: The results showed that adults with PWS had a low level of vocabulary (i.e., three to five standard deviations difference compared to neurotypical adults), poor reading skills (i.e., equivalent to the level of nine-year-olds), and less efficient lexical and non-lexical phonological processes. CONCLUSION: The present data suggest a global impairment in vocabulary and reading skills in adults with PWS. These findings might help clinicians to better understand the language abilities of these patients.