OBJECTIVE:To understand factors associated with successfully conducting longitudinal studies across early childhood by (i) describing the designs of Australian and New Zealand birth cohort studies; (ii) describing the breadth of variables studied; and (iii) identifying factors influencing study quality, productivity and contributions. METHODS:A systematic review was undertaken of 13 birth cohort studies. Data were collected from published papers and questionnaires administered to study investigators. RESULTS:These single cohort studies recruited children prior to their first birthday. Using an ecological model as an organizing framework, the studies were found to have contributed to knowledge about health and development in multiple domains and well beyond early childhood. Areas for increased focus included policy-relevant environmental factors such as child-care and rural/urban differences, and the influence of fathers, family factors, peers, social competence, and genetic factors. Investigators' responses indicated desires for an increased depth of data collection and stronger sampling designs. Data quality was enhanced by maintaining skilled staff and reduced by inadequate data for tracking study participants. Productivity ranged from 1 to 760 publications per study (median = 14.0). The most productive studies were those that had started before 1990, had representative samples, ongoing funding, and larger research teams. Policy impacts have included changed infant sleeping practices, reduced environmental lead emissions and regulated swimming pool safety standards. CONCLUSIONS:A suite of coordinated and nested studies could meet sampling needs and facilitate depth of inquiry. Stable, long-term funding is required to staff and maintain well-designed longitudinal studies that can address priority research areas and contribute to the development of health and social policy.