Between 1983 and 1998, age specific incidences of chickenpox derived from consultations with general practitioners taking part in the Royal College of General Practitioners Weekly Returns Service doubled in children aged 0 to 4 years, halved in children aged 5 to 14 years, and fell by almost a third in adults aged 15 to 44 years. This downward shift in age of contracting chickenpox may be a result of increased social contact between preschool children.