Although suicide remains a leading cause of death for adolescents, risk factors beyond diagnoses and suicide attempt history remain unclear. We examined whether cognitive style and temperament impact risk for an early, yet still clinically relevant and distressing, form of suicidality: active suicidal ideation. We used binary logistic regression to test whether brooding, inattention, and impulsivity predicted significantly increased risk for suicidal ideation in a sample of 134 twins, 46 of whom endorsed active suicidal ideation (i.e., probands), as well as probands’ cotwins and matched controls. When comparing probands with controls and controlling for depression diagnoses, brooding (B = 0.73, Odds Ratio [OR] = 2.07, p = 0.021), inattention (B = 1.09, OR = 2.98, p < 0.001), and impulsivity (B = 0.91, OR = 2.47, p = 0.001) differentiated probands from controls, individually. We compared probands with their cotwins using the same approach, which allowed us to account for variance in suicidal ideation risk related to twins’ shared, familial characteristics (e.g., prenatal environment, neighborhood); inattention was the only significant predictor of suicidal ideation risk (B = 0.66, OR = 1.93, p = 0.020). We then fit a logistic regression model that included all three predictors. Only inattention predicted significantly increased likelihood of suicidal ideation in proband versus controls and proband versus cotwin comparisons (B = 0.88, OR = 2.40, p = 0.024 and B = 0.67, OR = 1.96, p = 0.045, respectively). These results highlight the potential utility of examining novel, more proximal risk factors for suicidal ideation in addition to more established distal factors, like suicide attempt history and psychiatric diagnoses.