OBJECTIVES: A general societal preference for prioritizing treatment of rare diseases over common ones could provide a justification for accepting higher cost-effectiveness thresholds for orphan drugs. We attempt to determine whether such a preference exists. METHODS:  We surveyed a random sample of 1547 Norwegians aged 40-67. Respondents chose between funding treatment for a rare versus common disease and completed a person trade-off (PTO) exercise between the diseases for each of two scenarios: 1) identical per person costs, and 2) higher costs for the rare disease. Diseases were described identically with the exception of prevalence. Respondents were randomized to either no information or different amounts of information about disease severity (severe vs. moderate) and expected benefits of treatment (high vs. low). All respondents rated five statements concerning equity attitudes on a Likert-scale. RESULTS: A total of 68% of respondents agreed completely with the statement “rare disease patients should have equal right to treatment regardless of costs”. Faced with trade-offs, 11.3% of respondents favored treating the rare disease, 24.9% the common disease and 64.8% expressed indifference. When the rare disease entailed a higher opportunity cost, results were 7.4%, 45.3% and 47.3%, respectively. Framing (“extra funding” vs. “replace patients”) and amount of information about severity and treatment effectiveness had a small impact on preferences. CONCLUSIONS: Although there is strong support for general statements expressing a desire for equal treatment rights for rare disease patients, that support evaporates when individuals are faced with opportunity costs.