A retrospective approach has been adopted to investigate the frequency and duration of breast feeding and the time of gluten introduction in the diet in 216 celiac children and their healthy siblings of three different centers--Naples, Milan, and Turin. In this matched case-control study, the selected controls were healthy siblings of the cases. Children formula-fed from birth, or breast-fed for less than 30 days, were found to have a relative risk of developing symptoms of celiac disease four times higher than children breast-fed for more than 30 days (p less than 0.0001). To investigate more deeply the effect of the duration of breast feeding as a possible protecting factor, the linear trend for different periods of breast feeding was tested and found to be highly significant (G1: 18.3 with 1 df). Therefore, increased duration of breast feeding is associated with decreased risk of developing celiac symptoms. On the contrary, there was no apparent relationship between early introduction of gluten into the diet and frequency of celiac disease. Our findings are consistent with the hypothesis that a wider diffusion of breast feeding is a factor underlying the recently reported decrease of the incidence of celiac disease in children.