Objective: The purpose of this study was to test a research instrument that could possibly be used for longitudinal research on infant feeding and to report on the preliminary results from the data collected. Design: Mixed methods approach--cross-sectional survey and qualitative research. Setting: Mother-infant dyads in South West Sydney, Australia. Methods: Mother-infant dyads (n = 211) were recruited (response rate - 88%) within six weeks post-partum by Child and Family Health Nurses in Sydney South West. The parents were subsequently followed up by telephone interview when the child was four months or older. Cross-sectional data on infant feeding practices such as breast-feeding, formula feeding and introduction of solids and other fluids, bio-medical factors and socio-demographic data were recorded. Results: Of the 211 who agreed to participate, 187 were able to be followed up post-partum. The telephone questionnaire was not found to be intrusive and interviewers had no problems collecting data. Only 33% of mothers (n = 62) were found to be exclusively breastfeeding at four months post-partum. Higher maternal education was significantly associated with exclusive breastfeeding at four months. Maternal education, maternal country of birth, maternal age, gestational age and maternal antibiotic use post-partum were independent predictors of introduction of fluids. Female infants and residing in a rural/remote area were noted to be independent predictors of introduction of solid food at four months. Conclusions: The questionnaire was acceptable to parents and useful data was collected for future longitudinal studies in childhood nutrition and dental health. Given the substantial evidence on the benefits of breastfeeding and later introduction of complementary feeds, health promotion interventions should be targeted at the specific "at-risk" families. (Contains 1 figure and 6 tables.)