Abstract Background Visual hallucinations (VH) phenomenology in Lewy Body Disease (LBD) is heterogenous, including minor phenomena (passage, presence, illusions) and complex hallucinations. Neural substrates and mechanisms involved are still unclear. Here we investigated grey matter (GM) alterations associated with minor (MVH) and complex VH (CVH). Method LBD patients (n = 28) with VH and Healthy controls (HC‐n = 20) underwent MRI. We administered the North East Visual Hallucinations Interview (NEVHI), a semi‐structured interview assessing the phenomenology of VH, their duration and frequency. VH were clustered in MVH and CVH and treated as a patient’s trait. First we compared GM volume of LBD and HC. Then, multiple regressions were performed to disclose alterations associated with the duration, frequency and severity of MVH and CVH, including the opposite VH domain, total intracranial volume (TIV) and MMSE as nuisance regressors. Result We found a decreased GM volume in the bilateral fusiform gyrus (FG), in the left posterior cingulate and in the right inferior frontal gyrus in LBD compared to HC. We also found that CVH duration was negatively associated with GM volume in the left FG. We did not find any association with MVH phenomenology. Conclusion LBD patients showed GM alterations in ventral‐visual‐stream, default‐mode‐network and inhibitory regions compared to HC. Although the LBD versus HC comparison is not specific to VH, the regions identified have been implicated in VH in previous studies suggesting they may represent structural hallmarks of functional alterations in networks contributing to VH. When the association with VH phenomenology was tested, we did not find GM alterations associated with MVH. It is likely that these phenomena might be not associated with structural alterations but with functional alterations within visual networks. CVH were instead associated with decreased GM in FG. The atrophy in the FG may lead to a spontaneous activation of this region that sustain CVH duration, accounting for VH content (D’Antonio et al., 2022). These alterations may represent the predisposing condition to VH in LBD. According to the hodotopic model, VH phenomenology may help identify brain regions implicated and might reveal the substrates for cortical region/network dysfunctions occurring during VH state (ffytche et al., 2008).