OBJECTIVE Many patients with bipolar disorder in the United States experience a deteriorating course of illness despite naturalistic treatment in the community. We examined a variety of factors associated with this pattern of illness progression. METHOD From 1995 to 2002, we studied 634 adult outpatients with bipolar disorder (mean age of 40 years) emanating from 4 sites in the United States. Patients gave informed consent and completed a detailed questionnaire about demographic, vulnerability, and course-of-illness factors and indicated whether their illness had shown a pattern of increasing frequency or severity of manic or depressive episodes. Fifteen factors previously linked in the literature to a poor outcome were examined for their relationship to illness progression using Kruskal-Wallis test, followed by a 2-sample Wilcoxon rank sum (Mann-Whitney) test, χ(2), and logistical regression. RESULTS All of the putative poor prognosis factors occurred with a high incidence, and, with the exception of obesity, were significantly (P < .05) associated with illness progression. These factors included indicators of genetic and psychosocial risk and loss of social support, early onset, long delay to first treatment, anxiety and substance abuse comorbidity, rapid cycling in any year, and the occurrence of more than 20 prior episodes prior to entering the network. A greater number of factors were linearly associated with the likelihood of a progressively worsening course. CONCLUSIONS Multiple genetic, psychosocial, and illness factors were associated with a deteriorating course of bipolar disorder from onset to study entry in adulthood. The identification of these factors provides important targets for earlier and more effective therapeutic intervention in the hope of achieving a more benign course of bipolar disorder.