This study aimed to assess the protective effect of breastfeeding against gastrointestinal illness in infants during the first two years of life. The research was conducted in Dundee, Scotland, involving 750 pairs of mothers and infants, with 674 pairs remaining for analysis after excluding preterm, low birth weight, and special care cases. Health visitors made detailed observations of infant feeding and illness at various intervals over 24 months. The results showed that infants who were breastfed for at least 13 weeks had significantly fewer gastrointestinal illnesses compared to bottle-fed infants, with this protection persisting beyond the breastfeeding period. The reduction in illness was maintained even when supplements were introduced before 13 weeks and was accompanied by a lower rate of hospital admissions. However, no consistent protective effect was observed against other types of infections or conditions such as ear, eye, mouth, skin infections, infantile colic, eczema, or nappy rash. The study concluded that breastfeeding during the first 13 weeks of life confers long-lasting protection against gastrointestinal illness.This study aimed to assess the protective effect of breastfeeding against gastrointestinal illness in infants during the first two years of life. The research was conducted in Dundee, Scotland, involving 750 pairs of mothers and infants, with 674 pairs remaining for analysis after excluding preterm, low birth weight, and special care cases. Health visitors made detailed observations of infant feeding and illness at various intervals over 24 months. The results showed that infants who were breastfed for at least 13 weeks had significantly fewer gastrointestinal illnesses compared to bottle-fed infants, with this protection persisting beyond the breastfeeding period. The reduction in illness was maintained even when supplements were introduced before 13 weeks and was accompanied by a lower rate of hospital admissions. However, no consistent protective effect was observed against other types of infections or conditions such as ear, eye, mouth, skin infections, infantile colic, eczema, or nappy rash. The study concluded that breastfeeding during the first 13 weeks of life confers long-lasting protection against gastrointestinal illness.