Suicidal ideation (SI), a risk factor for suicide, is prevalent in internalizing psychopathologies, including depression and anxiety. Rumination and worry are well-studied repetitive negative thinking (RNT) constructs implicated in internalizing psychopathologies. These constructs have shared and distinct characteristics. However, the relationship between rumination and worry and their associations with SI are not fully understood in clinical samples. The present study used correlational and regression analysis to evaluate these relationships as a secondary data analysis in treatment-seeking participants with internalizing psychopathologies in two independent samples (Study 1:n=143; Study 2:n=133). Results showed about half of the participants endorsed SI (Study 1:n=79; Study 2:n=71). Correlations revealed a significant, positive relationship between rumination and worry. Regression results with SI as the dependent variable showed rumination significantly positively corresponded with SI in both studies. Post-hoc partial correlations controlling for symptom severity (depression, anxiety), worry, and age showed the rumination-SI relationship was maintained in both studies. Findings for worry and SI were inconsistent between studies. Findings indicate rumination, but not worry, could be a stable, unique contributor to SI in internalizing psychopathologies. It may be useful to incorporate RNT into suicide risk assessment for individuals with internalizing conditions.