Having more siblings has been shown to be associated with lower risk of ato
pic diseases. This might be due to the higher number of infections in large
r families. Because children attending day care centres have more respirato
ry infections, we analysed the association of number of siblings and day ca
re attendance in children aged 1-3 y with atopic disease in a cross section
al survey of 8387 schoolchildren aged 13-14 y and their parents in four reg
ions of Finland. Having no siblings, compared to three or more siblings, wa
s associated with significantly higher risk of Lifetime history of hay feve
r (odds ratios (OR) 1.53, 95% confidence interval (CI) 1.25-1.86) and atopi
c eczema (OR 1.28, 95%CI 1.04-1.56), and higher risk (ns) of doctor-diagnos
ed asthma ever (OR 1.26, 95%CI 0.85-1.88), Less strong associations were ob
served with the number of older siblings (birth order). No associations wer
e observed with current symptoms of these diseases during the last 12 mo. A
ttending a day care centre at the age of 1-3 y was not associated with decr
eased risk of any of the atopic diseases studied, but, in contrast to the h
ypothesis, was associated with slightly increased risk of current symptoms
of hay fever (OR 1.34, 95%CI 1.12-1.60). The present results suggest that o
ther factors than early childhood respiratory infections explain the associ
ation between number of siblings and future risk of atopic disease.