Introduction <p>Orthorexia Nervosa (ON), first described by Steven Bratman in 1997, refers to a pathological obsession with healthy eating, often resulting in restrictive dietary behaviors, nutritional deficiencies, and impaired psychosocial functioning. In the absence of standardized diagnostic criteria, this study aimed to develop and validate the Türkiye Orthorexia Nervosa Scale (TONS-29).</p> Methods <p>After excluding individuals with a diagnosed eating disorder (<i>n</i> = 7) or without informed consent (<i>n</i> = 8), a total of 720 adults (489 women, 231 men) participated. Scale development was guided by expert opinions from professionals in nutrition, psychiatric nursing, and Turkish linguistics. Construct validity was assessed through Exploratory Factor Analysis (EFA; <i>n</i> = 360) and Confirmatory Factor Analysis (CFA; <i>n</i> = 360) on randomly divided samples. A test-retest analysis was conducted with 128 participants.</p> Results <p>The final scale includes 29 items across five subfactors, with a Cronbach’s alpha of 0.941 and explained variance of 49.63%. Subdimension reliability was good to excellent (α = 0.724–0.908). CFA results indicated good model fit (chi-square/degrees of freedom [χ²/df] = 2.319, Root Mean Square Error of Approximation [RMSEA] = 0.061, Standardized Root Mean Square Residual [SRMR] = 0.052, Incremental Fit Index [IFI] = 0.907, Comparative Fit Index [CFI] = 0.906, Goodness of Fit Index [GFI] = 0.855, and Tucker–Lewis Index [TLI] = 0.907). The scale demonstrated temporal stability, with an intraclass correlation coefficient of 75.1% (95% CI: 0.647–0.824).</p> Conclusion <p>The findings support the TONS-29 as a valid and reliable tool for assessing ON tendencies in Turkish adults.</p>