The bipolar disorder is a chronic disorder with a high relapse rate, significant general disability, and psychosocial impairment. The cognitive deterioration is often considered as a basic characteristic of bipolar affective disorder. Emerging evidence suggests that neurodegeneration underlies bipolar disorder Our study aimed to investigate the cognitive deficits and serum BDNF in 1st and multiple euthymic phases in bipolar affective disorder (BPAD) patients and to correlate these cognitive deficits and serum BDNF with illness characteristics. 60 euthymic bipolar subjects, 30 patients were in the 1st euthymic phase, other 30 patients had two or more euthymic phase according to 10th International Classification of Psychiatric Disorders-Research Criteria (ICD10-RC) and 30 healthy control subjects were examined. Patients were euthymic for at least 3 months. All subjects were subjected to: 1- preliminary clinical psychiatric examination. 2- ICD 10 check list ,3- Young Mania Rating Scale( YMRS),4- Hamilton Rating Scale for Depression (HRSD) 5- Wechsler Adult Intelligence Scale (WAIS) , 6- Bender Gestalt test, 7- revised visual retention test (Benton test) .8- measurement of serum BDNF Results: Bipolar patients in1st euthymic phase achieved significantly lower score (more errors) on different used cognitive scales and tests, compared to control subjects. Bipolar patients in1st euthymic phase achieved significantly higher score (less errors) on different used cognitive scale and tests, compared to bipolar patients with multiple euthymic phase. Our results showed that duration of illness and number of episodes is inversely proportionate to cognitive functions performance. There was no statistical significant difference of serum BDNF among the studied groups. Conclusion and Recommendation: There were deficits in performances on visual memory, attention, concentration, delayed recall, executive function and general intelligence in euthymic bipolar patients. Bipolar patients (BP) in 1st euthymic phase were midway in the spectrum between control and bipolar patients with multiple euthymic phase regarding cognitive performance and serum BDNF. A severe course