Attrition from smoking cessation treatment by individuals with a history of major depression was investigated. An investigation of preinclusion attrition examined differences between eligible smokers who did (n = 258) and did not (n = 100) attend an initial assessment session. Postinclusion attrition was investigated by comparing early dropouts (n = 33), lale dropouts (n = 27), and treatment completers (n = 117). Those who failed to attend the assessment session were more likely to be female, to smoke cigarettes with higher nicotine content, and to have a history of psychotropic medication use. Early-treatment dropouts reported a higher smoking rate than late-treatment dropouts and endorsed more symptoms of depression than late dropouts and treatment completers. Results are compared with previous investigations of smoking cessation attrition, and implications for treatment and attrition prevention are discussed.Attrition from treatment poses a considerable problem for both researchers evaluating interventions (Howard, Cox, & Saunders, 1990) and clinicians delivering treatment (Stark, 1992). In studying attrition, investigators have found it useful to distinguish between preinclusion attrition-which occurs prior to entering a study, during screening or during intake evaluations-and postinclusion attrition, which occurs during treatment or posttreatment follow-ups (Howard et al., 1990). For example, evaluations of smoking cessation programs have noted preinclusion attrition rates of 30%-50% (Curry, Marlatt, Gordon, & Baer, 1988;Kviz, Crittenden, Madura, & Warnecke, 1994;Hall, Muñoz, & Reus, 1994) and postinclusion attrition rates that range from less than 10% (Curry, Thompson, Sexton, & Omenn, 1989;Zelman, Brandon, Jorenby, & Baker, 1992) to approximately 50% (Curry et al., 1988;Klesges et al., 1988).Although they are significant, these rates of attrition may be even higher in selected high-risk groups of smokers, such as those with psychiatric comorbidity. Disproportionately high rates of psychiatric comorbidity with cigarette smoking have been found in both adolescent (Brown, Lewinsohn, Seeley, & Wagner, 1996) and adult ) community samples. In adult smoking cessation programs, rates of past major depressive disorder (MDD) have ranged from 31% (Hall et al., 1994) to 61% (Glassman et al., 1988 smokers with a history of major depression have been shown to have elevated negative mood at pretreatment (Ginsberg, Hall, Reus, & Muñoz, 1995;Hall et al., 1994), to experience mood disturbance following cessation Ginsberg et al., 1995), and to relapse at higher rates than smokers without past MDD (Glassman et al., 1988;Glassman, 1993).As the overall prevalence of cigarette smoking decreases (Centers for Disease Control, 1994), those remaining smokers are likely to have more difficulty quitting because of factors such as psychiatric comorbidity and high nicotine dependence (Coambes, Kozlowski, & Ferrence, 1989;Hughes, 1993). Smoking cessation programs are increasingly faced with the prospect of delivering treatment ...