Objectives: People with childhood-onset disabilities are living into adulthood, and the prevalence of smoking and illicit drug use among adults with disabilities is high. We evaluated the relationship between disability status and age of disability onset, current cigarette smoking status, and heavy alcohol drinking. Methods: We conducted a secondary data analysis of the National Health Interview Survey (NHIS), a US survey on illness and disability. Among 2020 NHIS participants aged 22-80 years (n = 28 225), we compared self-reported prevalence of current cigarette smoking and heavy alcohol drinking among those with and without disabilities and among those with childhood- versus adult-onset disabilities. We used adjusted logistic regression analysis to calculate the adjusted odds ratios (AORs) of current smoking and heavy alcohol drinking based on disability status and age of disability onset. Results: Compared with adults without disabilities, adults with disabilities were significantly more likely to report current smoking (23.5% vs 11.2%; P < .001) and significantly less likely to report heavy alcohol drinking (5.3% vs 7.4%; P = .001). The prevalence of these behaviors did not vary significantly by age of disability onset. In adjusted logistic regression models, adults with disabilities had significantly higher odds of current smoking (AOR = 1.76; 95% CI, 1.53-2.03) and similar odds of heavy alcohol drinking (AOR = 0.82; 95% CI, 0.65-1.04) compared with adults without disabilities. The odds of these health behaviors did not vary significantly by age of disability onset. Conclusions: Adults with disabilities overall may be at high risk for these unhealthy behaviors, particularly smoking, regardless of age of disability onset. Routine screening and cessation counseling related to smoking and unhealthy alcohol use are important for all people with disabilities.