Purpose <p>Transmitted drug resistance (TDR) threatens the effectiveness of first-line antiretroviral therapy, yet contemporary regional data from the Aegean region of Türkiye remain limited. This study evaluated TDR prevalence, mutational profiles, and HIV-1 subtype distribution among treatment-naïve individuals.</p> Methods <p>We conducted a single-center retrospective cohort study at a tertiary referral center in İzmir, Türkiye, including adults with confirmed HIV-1 infection who were antiretroviral-naïve at baseline between January 2017 and December 2024. Genotypic resistance testing was performed before treatment initiation using Sanger sequencing. Resistance mutations were interpreted with Stanford HIVdb v10.1, and TDR was defined as a penalty score of ≥ 10 for at least one drug.</p> Results <p>A total of 163 individuals were included; the mean age was 38.16 ± 12.48 years, 91.4% were male, and subtype B was the most common clade (50.3%). Overall, 29 individuals (17.8%) had at least one resistance-associated mutation. NNRTI resistance predominated (15.3%), followed by NRTI (1.8%) and PI (0.6%); no INSTI mutations were detected. HIV-1 subtype F remained independently associated with antiretroviral resistance in multivariable logistic regression (OR 31.4, 95% CI 6.10–335.1; <i>p</i> &lt; 0.001). E138A was the most common NNRTI substitution (7.4%). S68G was the most frequent accessory mutation, identified in 41.7% of patients.</p> Conclusion <p>Transmitted drug resistance remains clinically relevant in treatment-naïve individuals in the Aegean region of Türkiye and is driven predominantly by NNRTI-associated mutations. The absence of baseline INSTI resistance supports the preserved activity of contemporary INSTI-based first-line regimens, while the observed association between subtype F and resistance warrants further molecular surveillance.</p>