Blood-Injection-Injury (BII) phobia is a particularly debilitating condition that has been largely ignored in the child literature. The present study examined the clinical phenomenology of BII phobia in 27 youths, relative to 25 youths with dog phobia—one of the most common and well-studied phobia subtypes in youth. Children were compared on measures of phobia severity, functional impairment, comorbidity, threat appraisals (danger expectancies and coping), focus of fear, and physiological responding, as well as vulnerability factors including disgust sensitivity and family history. Children and adolescents with BII phobia had greater diagnostic severity. In addition, they were more likely to have a comorbid diagnosis of a physical health condition, to report more exaggerated danger expectancies, and to report fears that focused more on physical symptoms (e.g., faintness and nausea) in comparison to youth with dog phobia. The present study advances knowledge relating to this poorly understood condition in youth.