BACKGROUND:Breast-feeding has shown to give a reduction in the risk of hospitalization due to respiratory tract infections and gastrointestinal conditions during the first two years of life. The association of breast-feeding with all admission causes and with fever of unknown origin (FUO) was analysed. METHODS:A case-reference study in Cantabria (northern Spain) was carried out. Cases (n=336) were hospitalized children aged less than 24 months at University of Cantabria Hospital; the reference was a 1:1 matched (by time from delivery to admission) sample of children from mothers delivering at the same hospital. Information on breast-feeding, socioeconomic variables and employment were obtained. Odds ratios (ORs), their 95% confidence intervals (CIs), and mean length of breast-feeding were estimated after adjusment for confounding variables. RESULTS:In the reference population, shorter duration of breast-feeding was associated with smoking, lower educational level, and less privileged social strata. The frequency of breast-feeding was higher in the reference than in the cases, 82.3% vs 75.6% (p=0.023). Significant negative trends were noted in univariate analyses between the length of breast-feeding and both all admission causes and FUO, although the statistical significance was lost after adjusting for confounding variables (educational level, social class, smoking, and use of incubator after delivery). The adjusted mean length of breast-feeding was shorter in hospitalized children < or = 6 months old for both all admission causes (40.6 +/- 5.4 vs 99.5 +/- 5.4, p < 0.001) and FUO (40.8 +/- 12.4 vs 91.7 +/- 12.4, p=0.006). CONCLUSION:Breast-feeding time is shorter in hospitalized children for both all admission causes and FUO.