Opera performances elicit strong emotional reactions in listeners. Yet, empirical demonstrations of these effects in situ are rare. Here we report a series of studies examining the emotional reactions of participants invited to the dress rehearsal of three different operas at the Geneva opera house before large audiences. Using a new affect checklist developed specifically for in situ studies of music performances, we asked participants to record (a) the intensity of 12 different types of affective reactions they experienced during selected scenes or (b) the frequency with which they experienced these emotions during specific acts or the opera as a whole. Results showed a high degree of specificity regarding the emotional impact of the operas as a whole and of individual scenes/acts. For one opera, Verdi’s Macbeth, we also asked participants to rate both the emotions they actually felt during the opera scenes and the emotions expressed by the music or the singers’ interpretation. Results confirm that spectators are clearly able to separate their own affective responses from what they perceive to be the emotions portrayed by the orchestra or on the stage. In addition, we evaluated the effect of different types of preperformance information sessions (on plot or music), as well as of participant personality and prior mood. Overall, the results demonstrate the feasibility of measuring highly differentiated emotional audience reactions to an opera performance with a brief validated checklist during actual performances in the opera house and the validity of self-reported emotions.