A c c e p t e d M a n u s c r i p t 2 Highlights We systematically reviewed the socioeconomic cost literature for 10 rare diseases. Direct and indirect costs incurred by patients, carers and society were searched. 77 studies were included with an unequal distribution of studies over disease types. Level of existing evidence is highest for diseases with available drug treatments. Indirect costs are in most cases of similar or higher magnitude than direct costs. found to range between 1-2 per 100,000 population (PWS, a sub-type of Histiocytosis, and EB) up to 42 per 100,000 population (Scleroderma). Overall, cost evidence on rare diseases appears to be very scarce (a total of 77 studies were identified across all diseases), with CF (n=29) and Haemophilia (n=22) being relatively well studied, compared to the other conditions, where very limited cost of illness information was available. In terms of data availability, total lifetime cost figures were found only across four diseases, and total annual costs (including indirect costs) across five diseases.Overall, data availability was found to correlate with the existence of a pharmaceutical treatment and indirect costs tended to account for a significant proportion of total costs.Although methodological variations prevent any detailed comparison between conditions, most of the rare diseases examined are associated with significant economic burden, both direct and indirect.