AIM: In most studies the methodology used to study growth in relation to breastfeeding patterns cannot ensure that exclusive breastfeeding has in fact occurred since birth. The aim of this study was to investigate the growth of healthy infants in Sweden in whom exclusive breastfeeding for the first 4-6 mo was ascertained through daily feeding records and to compare the results with the World Health Organization (WHO) "12-month breastfed pooled data set" and the Euro-Growth references for exclusively breastfed infants, as well as with the National Center for Health Statistics (NCHS)/WHO reference. METHODS: 147 exclusively breastfed infants and 325 non-exclusively breastfed Swedish infants, with a birthweight of > or = 3 kg, were included. The mothers had previous breastfed at least one infant for at least 4 mo. Weight was recorded fortnightly and length monthly. RESULTS: Infants exclusively breastfed since birth showed similar growth in weight and height to that of the non-exclusively breastfed infants. During the first 6 mo of life the growth of exclusively breastfed infants was also similar to that of the infants regularly receiving formula at 12-16 wk of age, mostly in addition to breast milk. The monthly growth increments were fairly similar to those of the "WHO pooled breastfed data set" and the Euro-Growth references for exclusively breastfed infants. CONCLUSION: In an affluent society truly exclusively breastfed infants seem to have the same growth during the first half year of life as non-exclusively breastfed infants with a high breastfeeding rate.