Background: Measuring societal preferences for rarity has been proposed to determine whether paying premium prices for orphan drugs is acceptable. Objective: To investigate societal preferences for rarity and how psychological factors affect such preferences. Method: A postal survey containing resource allocation dilemmas involving patients with a rare disease and patients with a common disease, equal in severity, was sent out to a randomly selected sample of the population in Sweden (return rate 42.3 %, n = 1270). Results: Overall, we find no evidence of a general preference for prioritizing treatment of rare disease patients over common diseases patients. When treatment costs were equal most respondents (42.7 %) were indifferent between the choice options. Preferences for prioritizing common disease patients over rare disease patients were more frequently displayed (33.3 % vs. 23.9 %). This tendency was, as expected, amplified when the rare disease was costlier to treat. The share of respondents choosing to treat the rare disease patients increased when presenting the patients in need of treatment in relative rather than absolute terms (proportion dominance). Surprisingly, identifiability did not increase preferences for rarity. Instead, identifying the rare disease patient made respondents more willing to prioritize the common disease patients. Respondents' level of education was significantly associated with choice -the lower the level of education the more likely they were to choose the rare option. Conclusion: We find no support for the existence of a general preference for rarity when setting health care priorities. Psychological effects, especially proportion dominance, are likely to play an important role for when preferences for rarity are expressed.