An exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were conducted on the Suicide Ideation Scale (SIS) with a large military clinical sample (total N = 3,072). The EFA identified a two-factor solution with the first factor (Resolved Plans/Preparation) accounting for 17.3% of the variance and the second (Suicidal Desire) accounting 15.1% of the variance. This 2-factor solution demonstrated a good fit to the data in the CFA. SIS construct validity and internal reliability data are also reported. The results of this study provide additional psychometric data for the SIS that support use of the measure in clinical work and research. Implications for theories related to suicide assessment and clinical practice are discussed.