This is a cross-sectional study which investigated the association between non-exclusive breastfeeding and maternal, paternal, obstetric and infant factors. Data on maternal, paternal, obstetric and infant factors were collected through face-to-face interview using a structured questionnaire from 498 mothers with four-week-old infants who attended government clinics in Klang district between 17 and 28 July 2006. The prevalence of non-exclusive breastfeeding at four weeks was 45.8%. Factors significantly associated with non-exclusive breastfeeding at four weeks included Indian ethnic mother (OR = 4.06), working mother (OR = 3.55), mother from high household income (OR = 1.90), mother who smokes (OR = 7.27), primiparous (OR = 1.97), infant not sharing a bed with mother (OR = 1.75) and infant born prematurely (OR = 7.69). Identification of risk factors should assist in targeting women who are at increased risk of non-exclusive breastfeeding.