Background <p>This study assessed the intersectionality of chronic diseases (CDs) and sociodemographic characteristics on mental health treatment utilization among New York City (NYC) adults.</p> Methods <p>We analyzed the 2019–2020 NYC Community Health Survey data, a representative sample of non-institutionalized adults. CDs included obesity, diabetes, hypertension, and asthma. Log-linear regression models assessed main and conditional effects of CDs and sociodemographic factors on mental health treatment utilization. Predicted probabilities illustrated significant interactions.</p> Results <p>Most of the 17,584 adults (weighted <i>N</i> = 6,437,401) were aged 25–44 years, female, heterosexual, non-Hispanic white, U.S.-born, married, college-educated, and employed. Regarding CD distribution, 49.6% had 0 CDs, 44.9% had 1–2 CDs, and 5.6% had more than 2 CDs. Approximately 16% of all adults reported using mental health treatment services in the past 12 months. In the main effects model, a dose-response relationship was observed between the number of CDs and the likelihood of receiving mental health treatment (<i>p</i> &lt; 0.001). Other factors associated with higher treatment rates included being aged 25–44, female, gay/lesbian/bisexual/other, non-Hispanic white, U.S.-born, unmarried, having higher education, being unemployed or not in the labor force, and having health insurance. The conditional effects model revealed significant interactions between CDs and race/ethnicity, sexual orientation, education level, and household poverty status (all <i>p</i> &lt; 0.05).</p> Conclusions <p>Findings highlight the complex interplay between CDs and sociodemographic factors in using mental health treatment among NYC adults. Although treatment rates generally increased with more CDs, this pattern varied significantly across key sociodemographic groups. These disparities underscore the need for targeted, intersectional approaches in mental health policy and program design.</p>