Knowledge that poor premorbid adjustment (PMA) precedes illness onset in many schizophrenia cases can facilitate early detection. Increasing consideration is being given to a similar early detection strategy for bipolar disorder (BPD). Results of this preliminary investigation comparing PMA in BPD (N = 53) and schizophrenia (N = 39) outpatients revealed a significant difference at the late adolescent (F[1,58] = 4.499, p = 0.038) stage only, with specific differences in two areas of PMA: adaptation to school (t [58] = 1.83, p = 0.036) and social sexual functioning (t [58] = 2.441, p = 0.009). However, mood state may affect some PMA ratings in BPD. Depression ratings were not correlated with reported late adolescent PMA, but a significant, positive correlation was found for the childhood stage (r = 0.32, p = 0.02). Findings fail to support a trend similar to schizophrenia of deteriorating PMA in BPD; however, the approach to investigations of PMA in BPD may need to be reconsidered.