Atypical patterns of face-scanning in individuals with autism spectrum disorder (ASD) may contribute to difficulties in social interactions, but there is little agreement regarding what exactly characterizes face-viewing in ASD. In addition, little research has examined how face-viewing is modulated by the emotional expression of the stimuli, in individuals with or without ASD. We used eye-tracking to explore viewing patterns during perception of dynamic emotional facial expressions in relatively large groups of individuals with (n = 57) and without ASD (n = 58) and examined diagnostic- and age-related effects, after subgrouping children and adolescents (≤18 years), on the one hand, and adults (>18 years), on the other. Results showed that children/adolescents with ASD fixated the mouth of happy and angry faces less than their typically developing (TD) peers, and conversely looked more to the eyes of happy faces. Moreover, while all groups fixated the mouth in happy faces more than in other expressions, children/adolescents with ASD did relatively less so. Correlation analysis showed a similar lack of relative orientation towards the mouth of smiling faces in TD children/adolescents with high autistic traits, as measured by the Autism-Spectrum Quotient (AQ). Among adults, participants with ASD only attended less to the eyes for neutral faces. Our study shows that the emotional content of a face influences gaze behaviour, and that this effect is not fully developed in children/adolescents with ASD. Interestingly, this lack of differentiation observed in the younger ASD group was also seen in younger TD individuals with higher AQ scores. Autism Res 2017, 10: 901-910. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.