Primary care presentations at emergency departments (EDs) have been the subject of much attention in recent years. This paper is a demographic analysis using administrative data from the Emergency Department Information System (EDIS) for 2005 of such presentations in New South Wales EDs and of self-reported reasons for presentation. Age and sex differences in the reasons given by patients for such presentations are analysed using data from a survey of patients conducted in a subset of EDs in 2004. The rate of "potential primary care" presentations varies greatly with age and to a lesser extent with sex. Almost half (47%) of these presentations are made by people under 25 years of age. Children aged 0-4 years account for 14% of the total. The pattern is distinctly different to the corresponding rate of ED presentations that do not fit the "potential primary care" definition. Reasons given for "potential primary care" presentations are consistent across all age groups, reflecting self-assessed urgency, access to diagnostics and self-assessed complexity. Older "primary care" patients are particularly unlikely to give reasons associated with GP affordability or availability for their presentations. Young adults' responses are consistent with the overall population, and children under the age of five seem most susceptible to availability issues.