Gaze avoidance is a hallmark behavioral feature of fragile X syndrome (FXS), but little is known about whether abnormalities in the visual processing of faces, including disrupted autonomic reactivity, may underlie this behavior. Eye tracking was used to record fixations and pupil diameter while adolescents and young adults with FXS and sex- and age-matched typically developing controls passively viewed photographs of faces containing either a calm, happy, or fearful expression, preceded by a scrambled face matched on luminance. Results provide quantitative evidence for significant differences in gaze patterns and increased pupillary reactivity when individuals with FXS passively view static faces. Such abnormalities have significant implications in terms of understanding causes of gaze avoidance observed in individuals with FXS.