We have examined 18 children with a similar laterothoracic exanthem that appears to represent a distinct entity.Our purpose was to describe the characteristic signs and clinical course of this eruption and its epidemiology data.We observed the clinical course of the eruption in each child.The eruption has characteristic features. It occurs in a homogeneous age group (mean 23.3 months). It is initially unilateral and localized close to the axilla. The basic lesion is eczematous or scarlatiniform. The eruption evolves in two phases: it spreads centrifugally during the first 8 days and becomes more widespread on the tenth to fifteenth days, with predominant involvement on the half of the body initially affected. The lesions resolve spontaneously within 4 weeks. The long-term course is uneventful.The similarity of the cases suggests the existence of a new clinical entity. Many features favor a viral origin.