Exclusive breastfeeding was studied among 506 infants in Uppsala, Sweden, based on daily recordings during the first 6 mo. The mothers had previously breastfed at least one infant for at least 4 mo. Most of the mothers considered that they breastfed on demand. Wide variations in breastfeeding frequency and suckling duration were found both between different infants and in the individual infant over time. At 2 wk, the mean frequency of daytime feeds (based on one 13-d record) between different infants ranged from 2.9 to 10.8 and night-time feeds from 1.0 to 5.1. The daytime suckling duration (based on one 24-h record) ranged from 20 min to 4h 35 min and night-time duration from 0 to 2h 8 min. At any given age, a maximum of only 2% of the infants were not breastfed during the night. At 4 mo, 95% of the infants were breastfeeding and 40% were exclusively breastfed at this age. Longer breastfeeding duration and longer duration of exclusive breastfeeding were both associated with higher frequency of breastfeeds, longer breastfeeding of the previous child and higher education. No gender differences were found. Maternal smoking was associated with shorter duration of exclusive breastfeeding, and pacifier use was associated with shorter duration of both exclusive breastfeeding and total breastfeeding. This study confirms that every mother-infant pair needs to be understood as a unique dyad throughout lactation. These data demonstrate a wide range of patterns among women who are exclusively breastfeeding and indicate that it would be inappropriate to put pressure on individual families to adopt preconceived patterns of infant feeding.