['To investigate the impact of maternal diet during breastfeeding on atopic sensitization of infants at risk.', 'Prospective cohort study.', 'Turku University Central Hospital, Finland.', 'Altogether 114 infants with a family history of atopic disease were followed during their first year of life. The mothers completed a 4 day food record during breastfeeding just before the infants were 3 months old. Atopic sensitization of the infants was determined by a positive skin prick test result at 12 months.', 'Positive skin prick test reactivity to at least one antigen was detected in 27/114 (24%) infants at 12 months. The energy intake of the mothers was low, mean 8.0 MJ/day (95% CI 7.7-8. 3), and the proportion of energy derived from fat was high, mean 36. 6 E% (95% CI 35.6-37.6). Atopic mothers had a higher intake of total fat and saturated fat and a lower intake of carbohydrate as a percentage of total energy intake than non-atopic mothers; P=0.017, P=0.050, P=0.004 respectively. Maternal intake of saturated fat during breastfeeding was associated with atopic sensitization of the infant, OR=1.16 (95% CI 1.001-1.36); P=0.048 irrespective of the maternal atopic status.'] Is maternal diet rich in saturated fat during breastfeeding associated with atopic sensitization of the infant?