Poor diet quality is linked to non-communicable diseases and mortality. Area deprivation is an important determinant of diet. Whether small area deprivation influences the spatial distribution of diet quality remains unknown. We aimed to assess the spatial dependence of diet quality and its association with local-scale deprivation in adults. We used data from the 2016–2019 waves of the population-based Bus Santé Study in Geneva (n = 4453). We assessed diet quality through the Alternate Healthy Eating Index (AHEI), and its spatial dependence through the Local Indicators of Spatial Association (LISA or Local Moran's I). Bivariate LISA analyses and Geographically Weighted Regression models were used to assess associations with sociodemographic variables and small-area deprivation. We used regression models of diet and metabolic health variables to confirm the validity of the low diet quality spatial clustering. We included 4248 participants (mean age 47 ± 14, 50·7% women). We found a mean AHEI score of 35·2 (SD 10·8). 40% of the participants fell into a low diet quality category. Diet quality was spatially patterned across the Canton of Geneva, with identified clusters of lower diet quality (mean AHEI score 27·8 ± 6·24) and higher diet quality (mean AHEI score 43·8 ± 6·8). Clusters of low diet quality persisted after adjusting for individual-level variables. The largest low diet quality cluster was associated with higher local deprivation. Our study sheds light on the role of local-scale deprivation as an independent contextual determinant of diet in a high-income European city.