The Prader-Willi syndrome is a rare, complex, and genetically determined neuro-developmental disorder. The subjects have their own individual characteristics; however share in common particular physical features and specific cognitive strengths and weaknesses. These change across the lifespan and make up the physical and behavioural “phenotype” of the syndrome. Learning difficulties are common and range the whole spectrum, from mild to severe. Most subjects find reading, spelling and especially mathematics very difficult. With age, certain behaviours become more evident, for instance repetitive and ritualistic behaviour in older children and adults. According to the literature subjects score moderate to high on subscales measuring compulsory behaviour. The literature on cognitive functioning and achievement of individuals with PWS is heterogeneous, concerning the pedagogical and psychological aspects in adults, the literature is sparse. This study was based on individuals with genetically verified PWS included in the Nordic Prader-Willi study. By means of a computer based cognitive test (CogState), the aim of the present pilot study was, on a cross-sectional basis, to analyse aspects of the adults working memory. Further to relate the findings to existing literature concentrating on cognitive aspects of the syndrome and especially discussing aspects of working memory. Moreover, reflections concerning life long development and learning were based on the results. We found that adults with PWS have significantly decreased elements of working memory compared to normative data. In general, the subjects had median scores within two standard deviations below the normal mean, however with huge differences between the tests performed. Moreover, extensive inter-individual ranges were observed. Females did significantly better than male participants in some of the items. Related to BMI, the more obese had a slightly better performance of working memory than the less obese.In conclusion, adults with PWS were both positive and corporative, in this time limited, motivating, and visual based cognitive test situation. In general; the sample had markedly decreased working memory, as detected with the CogState battery. The impairment for all items was of major magnitude, however the impairment of visual memory was less pronounced. This should be taking into account, when teaching strategies and learning are considered. The visual pathway is obviously the best functioning and should be used in educational settings and when giving general information.