An empirical research was carried out in order to analyze intonation as a quality criterion in simultaneous interpreting. As opposed to previous studies on quality expectations, this paper focusses on one single criterion, aiming at finding out the discrepancies in the relative weight given to intonation between the subject’s expectation pattern and the actual impact of intonation on their assessment. With this in mind, the author scrutinizes the most frequent level of monotony in simultaneous interpreting, as well as the effects of the interpreter’s intonation on the audience when assessing simultaneous interpreting performances. The results of this study show that monotonous intonation is common in simultaneous interpreting and suggest two basic ways of conceptualization linking the intonation to the effects on the simultaneous interpreting. On the one hand, the psychological effects of the interpreter’s monotonous intonation on the audience. On the other, those effects that directly influence another quality criterion, sense consistency. The latter stresses the relation between the non-verbal criterion intonation and the verbal criteria cohesion and sense consistency, which have been consistently identified as the most important ones in most of the surveys on quality expectations.