This study investigates strategic voting for small parties in proportional representationsystems, in previous work sometimes referred to as threshold insurance voting (Cox,1997). Starting from theories of rational voting (Downs, 1957), three conditions for threshold insurance voting are developed: the voter considers potential government outcomes, votes fora party at risk of falling below an electoral threshold, and votes for another party than his orher most preferred one. The conditions are tested on the case of the 2010 Swedish general election. Using extensive data material and a conditional logit model of vote choice, the resultsshow that in this election voters cast strategic votes for at least one of the small parties, the Christian Democrats which was included in the incumbent government coalition.