To characterize more precisely the phenotypic complexity of this disorder, we have developed a spectrum model of psychiatric illness using a broader conceptualization of mood disorders and an integrated view of common comorbidities, anchored in the Mood and Anxiety Spectrum Assessments (Cassano et al. 1997; Cassano et al in press). This refined description of patient variability (or phenotypes) should lead to improved understanding of the variability in treatment outcomes among patients suffering from bipolar disorder and eventually to creating appropriate first-line treatments for patients who present with specific clinical phenotypes.