Background: We examined patterns of alcohol use among mothers with infants in the UK focusing on (i) common (“majority”) patterns of alcohol use (frequency and quantity) and (ii) associated social factors. Methods: We analyzed data from 15,510 mothers who took part in waves 1 and 2 of the millennium cohort study in 2000/1. Nine months after birth, mothers reported their frequency and quantity of alcohol use, along with information on social circumstances. Logistic regression, carried out in 2011, helped identify the social factors associated with majority patterns of alcohol use. Results: Majority patterns of alcohol use were: Infrequent drinking (never/<1/week), infrequent light drinking (1 unit/day, <1/week), and frequent light drinking (<14 units/week). In mutually adjusted models, infrequent drinking was associated with childhood, educational, and income disadvantage, and younger age at first birth. Infrequent light drinking was associated with educational and income disadvantage, economic inactivity, and marriage. Frequent light drinking was associated with marriage and fewer children in the household. Conclusions: Among mothers in the UK, the majority drank infrequent small quantities. Positive social gradients were evident for frequency of alcohol use among socially advantaged mothers.