Objective: Alcohol use disorders (AUDs) and suicidal ideation (SI) co-occur, yet few studies have investigated the risk and protective factors that influence their comorbidity. Method: Data from 3,787 twin women ages 18-27 years were analyzed. AUD was defined as a lifetime history of alcohol abuse or dependence as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. SI was coded as a lifetime report of any SI, and all subjects were queried about SI. Subjects were divided into those with neither AUD nor SI (AUD-SI-), those with AUD but no SI (AUD+SI-), those with SI but no AUD (AUD-SI+), and those with comorbid AUD and SI (AUD+SI+). Association with multiple measures of psychopathology, negative life events, personality, and family history was assessed using multinomial logistic regression. Results: Women with AUD were at 3.1 (95% confidence interval [2.5, 3.8]) odds of also reporting a lifetime history of SI. Psychopathology and negative life events were consistently high in the AUD+SI+ group. AUD+SI+ women also were more likely to report drinking to cope. Substance use was more common in the AUD+SI- versus the AUD-SI+ women, whereas major depressive disorder, social phobia, and panic attacks were more commonly reported by the AUD-SI+ versus the AUD+SI- women. Conclusions: The comorbidity between AUD and SI is characterized in young women by co-occurring psychopathology, drinking to cope, and negative life events.