The stock of effective antibiotics is a potentially renewable but currently finite common resource. Depletion, through the development of resistance, which occurs with all use, poses a large and growing menace to public health, but prudent antibiotics use can delay the spread of resistance. Individuals’ preferences may be of importance for the possibility to overcome social dilemmas, such as common resource conservation. In this study the role of otherregarding preferences and time preferences in the use of antibiotics is examined in a field experiment at clinics in the County of Stockholm, Sweden. The results indicate that altruism, as measured by willingness to give to a charity, is associated with less antibiotics use. Time preferences do not appear to play a role. Overconfidence in the effectiveness of antibiotics is widespread, and significantly associated with antibiotics use.