While the economic burden imposed by dementia is well-documented, findings are mixed on health care use for those with mild cognitive impairment (MCI). Our objective was to analyse annual, non-hospital medical and pharmaceutical use patterns for older people with undiagnosed MCI and diagnosed dementia, living in the Australian community. We analysed panel data from a community sample, the Sydney Memory and Ageing Study (Australia), linked to administrative data on health care use, using two-part models to estimate the probability of using health care and the annual costs incurred by study participants. People with MCI, unaware of their diagnoses, were significantly less likely to incur annual pathology and diagnostic imaging costs relative to cognitively normal individuals. This effect was concentrated in individuals with MCI who had non-amnestic symptoms, lived alone, or had limited carer support. Compared to cognitively normal individuals, people with MCI were predicted to have slightly lower annual costs for broad medical care categories related to the management and diagnosis of cognitive impairment, and people with dementia, substantially higher professional attendances, and pharmaceutical costs. These findings were consistent across estimation models adjusting for attrition over the study. Diagnosis and symptom management in primary care may enable individuals with MCI to improve their quality of life and prevent more costly future health care use. However, our study found potential gaps in medical service use for people with undiagnosed MCI in the community, especially when they had less support or did not have memory symptoms. Primary care services may need to better diagnose and target these individuals.