Three studies were conducted with the aim of developing a new Swedish self-report measure of core affect (the Swedish Core Affect Scale or SCAS). In Study 1,122 participants rated their current mood on 24 unipolar adjective scales. A revised set of 12 bipolar adjective scales was evaluated in Study 2 employing 96 participants who rated their current mood before and after a mood-inducing naturally occurring event. A slightly revised set of adjective scales was used in Study 3, in which another 96 participants rated several induced moods. The results showed that the adjective scale ratings could be aggregated as reliable measures of the independent valence and activation dimensions proposed in the affect circumplex, and that the aggregated measures discriminated mood differences within and between individuals.