Background: Acute respiratory infections and diarrhea remain the leading causes of infant morbidity and mortality, with a high burden of both pneunomia and diarrhea in South-East Asia. The aim of the study was to determine antenatal and early infant predictive factors for severe morbidity episodes during the first 6 months of life in Ha Nam province, Vietnam. Methods: A prospective cohort study of 1049 infants, born to women who had previously participated in a cluster randomized controlled trial of antenatal micronutrient supplementation in rural Vietnam, was undertaken between 28th September 2010 and 8th Jan 2012. Infants were followed until 6 months of age, and the outcome measure was inpatient admission for suspected pneumonia or diarrheal illness during the first 6 months of life. Risk factors were assessed using univariable logistic regression and multiple logistic regression. Results: Of the 1049 infants seen at 6 months of age, 8.8 required inpatient admission for suspected pneumonia and 4 of infants required inpatient admission for diarrheal illness. One third of infants (32.8 ) were exclusively breast fed at 6 weeks of age. Exclusive breast feeding at 6 weeks of age significantly reduced the odds of inpatient admission for suspected pneumomia (Odds Ratio (OR) 0.39, 95 Confidence Interval (CI) 0.20 to 0.75) and diarrheal illness (OR 0.37, 95 CI 0.15 to 0.88). Conclusions: Exclusive breast feeding in early infancy reduces the risk of severe illness from diarrhea and suspected pneumonia. Public health programs to reduce the burden of inpatient admission from diarrheal and respiratory illness in rural Vietnam should address barriers to exclusive breast feeding.