The aim of this study was to identify the breastfeeding attitudes and knowledge of a sample of Australian general practice (GP) registrars and investigate how confident and effective they thought their interactions with breastfeeding women were. Between February and May 2007, a 90-item questionnaire containing demographic, attitude, and knowledge items was distributed to final-year Australian GP registrars. The mean attitude score (5 = maximum score) was 3.99. The mean knowledge score (5 = maximum score) was 3.40, indicating some degree of breastfeeding knowledge. However, 40% of the knowledge items were answered incorrectly by the majority of participants. Approximately 40% of the cohort were confident and thought they were effective assisting breastfeeding women. Having more than 26 weeks personal experience with breastfeeding (self or partner) increased breastfeeding knowledge, attitudes, confidence, and effectiveness. Further targeted training is needed to improve Australian GP registrars' breastfeeding knowledge, attitudes, confidence, and effectiveness.