Lead is a highly toxic metal and a very strong poison. Lead poisoning is a serious and sometimes fatal condition. It occurs when lead builds up in the body. Lead is found in lead-based paints, including paint on the walls of old houses and toys. Lead poisoning usually occurs over a period of months or years. It can cause severe mental and physical impairment. Young children are most vulnerable. Children get lead in their bodies by putting the lead containing objects in their mouths.