Aim We determined if differences in renal function, even within normal levels, influenced hippocampal volume (HCV) and cognition. Methods Cognitively normal (CN) and mild cognitive impairment (MCI) subjects with eGFR ≥ 60 ml/min/1.73m2 were selected from the ADNI database (N = 1,269) and divided into three groups (eGFR 60–75, 75–90 and ≥90). Associations between eGFR, HCV and cognition scores were examined using regression methods, and random‐coefficient models. The relationship between various factors, such as vascular burden and brain amyloid deposition, were investigated using path analysis. Results Higher eGFR was associated with larger HCVs and better cognition in all subjects at baseline. In MCI subjects, hippocampal atrophy in the eGFR ≥ 90 group progressed at just half the rate of the eGFR 75–90 group (P = .006), and was also somewhat slower than the eGFR 60–75 group (P = .08). A comprehensive path model linking eGFR, HCV and cognition, and integrating vascular burden and amyloid deposition, is proposed. Conclusions Higher renal function was associated with slower hippocampal atrophy and cognitive decline even within normal levels of renal function. This relationship was mediated mainly through cardiovascular risk burden and amyloid deposition. Further studies examining neuroinflammation are needed. Geriatr Gerontol Int 2017; ••: ••– ••.