[Thrombocytosis and essential thrombocythemia in childhood].

Thrombocytosis is frequently observed in pediatric patients. Among them the secondary thrombocytosis are the most frequent and result from several causes. The rarely primary thrombocytosis can be either constitutive (and often familial) or acquired (essential thrombocythemia). The purpose of this article is to give diagnostic orientation and to suggest which biological tests should be performed.