Cognitive models of social phobia (SP) and empirical evidence in adults suggest that affected individuals overestimate arousal symptoms such as heart rate (HR) during social stress and worry about their visibility in public. To date, little is known about these aspects in childhood social anxiety, an important precursor of the disorder. We assessed perception of--and worry about--HR visibility, actual HR, and subjective anxiety during public speaking in high socially anxious (HSA; n = 20) and low socially anxious (LSA; n = 20) Caucasian children, aged 10 to 12 years. Symptom visibility was manipulated by making a nonveridical HR feedback tone audible only to the participant (private condition, HR sounds via headphone) or to participant and observers (public condition, HR sounds via speakers). Further, we assessed interoceptive accuracy in a heartbeat counting task. As expected, HSA children perceived their HR as higher than LSA children in both private and public conditions despite similar actual HR and comparable interoceptive accuracy. Public feedback led to more worry about HR visibility only in HSA but not in LSA children. Biased perception and interpretation of bodily anxiety symptoms during social stress manifests early in social anxiety and might therefore play a crucial role in the aggravation of social anxiety and the development of SP. We discuss implications for current theory, clinical practice, and prevention. (Contains 1 table, 2 figures, and 5 footnotes.)