Exclusive breast-feeding (EBF) seems to reduce risk of allergies in the western countries, but there are few reports from developing countries. The purpose of this study was to assess the effect of EBF on the development of allergic diseases and eczema in a developing country. This is a cross-sectional survey done at the well-baby clinics of 11 primary health centers, Hamad Medical Corporation, Qatar. A multistage sampling design was used and a representative sample of 1500 children (0-5 years old) and mothers (18-47 years old) were surveyed between October 2006 and September 2007. Of them, 1278 mothers (85.2%) participated in the study. A confidential, anonymous questionnaire assessing breast-feeding and allergic diseases was completed by mothers bringing children for immunization. Questionnaire included allergic rhinitis, wheezing, eczema, type and duration of breast-feeding, parental smoking habits, number of siblings, family income, maternal education, and parental allergies. Univariate and multivariate statistical methods were performed for statistical analysis. More than one-half of the infants (59.3%) were on EBF. Length of breast-feeding was associated with maternal age. Prevalence of eczema (19.4%), allergic rhinitis (22.6%), and wheezing (12.7%) were significantly less frequent in those with prolonged (>6 months) compared with short-term fed infants. The association between EBF and eczema tended to be similar in children with a positive family history of atopy (p < 0.001) and eczema (p < 0.001) compared with those without. In children of developing countries, prolonged breast-feeding reduces the risk of developing allergic diseases and eczema even in the presence of maternal allergy, where it might be a practical, effective preventive measure.