We report on the study of gazes, conducted on children with pervasive developmental disorders (PDD), by using a novel head-mounted eye-tracking device called the WearCam. Due to the portable nature of the WearCam, we are able to monitor naturalistic interactions between the children and adults. The study involved a group of 3- to 11-year-old children (n=13) with PDD compared to a group of typically developing (TD) children (n=13) between 2- and 6-years old. We found significant differences between the two groups, in terms of the proportion and the frequency of episodes of directly looking at faces during the whole set of experiments. We also conducted a differentiated analysis, in two social conditions, of the gaze patterns directed to an adult's face when the adult addressed the child either verbally or through facial expression of emotion. We observe that children with PDD show a marked tendency to look more at the face of the adult when she makes facial expressions rather than when she speaks.