The clinical characteristics of bipolar I disorder (BD1) have prognostic and therapeutic importance. The aim of this study was to examine the effect of demographic and clinical variables on the course of BD1. We reviewed the case notes of all BD1 patients (n = 63) receiving treatment in a London psychiatric service during a 1-month period. Depressive and manic onsets were equally likely without any gender difference. The earlier the age of onset, the more likely it was for patients to experience psychotic features. Only depressive onsets predicted a higher number of episodes of the same polarity. Male gender and substance abuse were associated with younger age at first presentation, while women with co-morbid substance abuse had more manic episodes. Male patients were more likely than females to be unemployed or single.