The characteristics of 4 groups of bipolar subjects categorised as substance abuse only, substance abuse associated with other Axis I disorders, nonsubstance abuse Axis I comorbidity, & no psychiatric comorbidity, were investigated. By comparison with the group with no psychiatric comorbidity, the group with substance abuse associated with other Axis I disorders had an earlier age at onset of mood disorder, a more frequent onset with a mixed state, & a higher risk of suicide. (22 refs.)