AbstractBackgroundAlzheimer’s disease (AD) is associated with poorer memory and reduced grey matter volume. Non‐amnestic cognition and white matter (WM) changes are an alternative line of enquiry and may reveal earlier changes. We investigated how inhibitory control relates to the superior longitudinal fasciculus (SLF) in groups at‐risk of AD.MethodParticipants (n = 229; aged > 55 years) from the Dementia Prevention Research Clinic, New Zealand were classified as control (C; n = 35), subjective cognitive decline (SCD; n = 60), single‐domain amnestic MCI (aMCI; n = 55), multiple‐domain MCI (mMCI; n = 52), and AD (n = 27). Using diffusion MRI, we measured WM fiber density (FD), fiber cross‐section (FC), and fiber density cross‐section (FDC) in the SLF (SLF1, SLF2, SLF3 in each hemisphere, Figure 1). We also measured inhibition (Trail‐Making B, Stroop Inhibition, Switching, Hayling Incongruency), generativity (Letter Fluency, Category Fluency), and processing speed (Trail‐Making A, Stroop Color Naming, Word Reading).ResultMultivariate analyses showed impaired cognition across groups, with stronger impairments in inhibition (F(4, 206) = 5.41, p < .001; Wilk’s Λ = 0.55, η2p = 0.12) than processing speed (F(4, 217) = 2.45, p = .001; Wilk’s Λ = 0.84, η2p = 0.04). Generativity was also impaired across groups (p < .01). Significant variation in FD was found across groups in all SLF tracts, except for left SLF1 (Figure 2a). Between‐group differences (Figure 2c) included greater FD in C in the right SLF2 than mMCI (p = .04, d = 0.58), in the right SLF3 than SCD (p = .04, d = 0.57) and mMCI (p = .003, d = 0.77), and in the left SLF3 than SCD (p = .04, d = 0.65), mMCI (p = .01, d = 0.69), and AD (p = .02, d = 0.67). Two separate partial least‐squares analyses showed that poorer inhibition, but not processing speed, was associated with lower FD in the SLF (Figure 3).ConclusionOverall, we found that reduced FD in the SLF was associated with poorer inhibitory control in risk groups of AD. Therefore, WM alterations in the SLF may provide an early marker in AD.