Objectives: To determine the frequency of 14 discipline strategies used by mothers (n = 564) and fathers (n = 335) in caring for their six-month old infant. Methods: Data on discipline practices were obtained from families participating in an obesity prevention trial (Prevention of Overweight in Infancy). Each parent was asked to indicate the frequency of using 14 different discipline strategies during the previous week with their infant. Associations between the use of these strategies and parity, deprivation, parental ethnicity, depression symptoms and infant sex were investigated. Results: Parents reported using both positive (mean: 8.8 for mothers and 7.9 for partners) and negative (0.7 for mothers and 0.7 for partners) strategies over the past week. At six months, positive strategies such as smiling, praising and distraction were most commonly reported (=87% for both mothers and partners), negative strategies such as smacking, time out and shouting being reported infrequently (=8% for all). Discipline requiring a level of cognitive understanding not developed at six months was reasonably common, including reasoning (17.7% for mothers, 23.4% for partners), negotiation (6.2%, 11.7%) and ignoring (26%, 19%). Multivariate analysis demonstrated that mothers with more than one child had a lower positive discipline index than those with only one child (difference, 95% C.I.: 1.05 (0.57, 1.54). An increase of one point on the 10-point hostile parenting scale was associated with an increase of 0.18 (0.04, 0.31) for the mothers and 0.47 (0.23, 0.70) for partners on the negative strategy index. Conclusions: Discipline strategies emerge early in infancy and are associated with family size and parental hostility.