In developed communities, the effect of exclusive breastfeeding (EBF) is encouraged since it has been found to be protective against infantile diarrhea. In a newly developing Qatar, modern water supply and sanitation facilities have become available to everyone during the last two decades. The objectives of the current study were to explore the relationships between breastfeeding and diarrhea and to assess the effect of EBF on the risk reduction of diarrhea in children aged 1-5 years. This is a cross-sectional survey conducted in the Well-Baby clinics and pediatric clinics in the 11 Primary Health Care (PHC) Centers and Hamad General Hospital, Hamad Medical Corporation, Qatar. A multistage sampling design was used, and a representative sample of 1500 Qatari infants and pre-school children in the age group of 1-5 years and mothers aged between 18 to 47 years were surveyed during the period from October 2006 to September 2007; 1,278 mothers agreed to participate in this study, with a response rate of 85.2%. The sociodemographic characteristics, feeding modes and diarrhea morbidity were collected from the parents of the children during the interview. Of the 1,278 infants studied, more than half (59.3%) were EBF, followed by those partially breastfed (28.3%), and finally the formula fed (12.4%). The duration of EBF was 11.4+/-6.7 months (mean+/-SD) and the duration of partial breastfeeding with bottled milk was 9.2+/-4.1 months (mean+/-SD), and the difference was statistically significant (p<0.0010). When compared to the EBF infants, the risk of diarrhea was higher and statistically significant in both the partially breastfed (48.7% vs 32.5%) and in the non-EBF (37.3% vs 32.5%, p<0.001). Upper respiratory tract infection (URTI), short duration of breastfeeding, level of maternal education, and sterilization of bottles were considered as predictors. These results indicate that in Qatar, breastfeeding plays an important role in reducing the incidence and severity of infantile diarrhea. This observation is particularly important given the growing concern that, as an unwanted effect of 'modernization', breastfeeding is on the decline in Qatar and comparable populations elsewhere.