Background: There is an increasing focus on the impact of psychosocial factors and stressors on the course of bipolar affective disorder. The life event research has revealed many biases and the results are conflicting. In a prospective study we examined the relationship between life events and affective phases in a group of bipolar patients with a long duration of the disease. Methods: A group of patients with at least three admissions to hospital for bipolar disorder was followed every 3 months for up to 3 years. At each examination an evaluation of affective phase was made according to the Hamilton Depression Scale, the Newcastle Depression Rating Scale and the Bech‐Rafaelsen Mania Rating Scale. Moreover, the patients were rated according to the Paykel Life Events Scale. Their current medical treatment was noted. Results: Fifty‐six patients (19 men and 37 women) were included in the study. Women experienced a significantly higher number of life events than men. In 21% of the 353 examinations of women, a new phase was preceded by life events whereas this was the case only in 8% of the 152 examinations of men. In 13% of the male examinations the patients were in a manic phase and in 5% in a depressive phase. In 5% of the female examinations the patients were in a manic phase and in 15% in a depressive phase. Half of the women's depressive phases were preceded by life events, but none of the depressive phases of men. The categories of life events preceding the depressive phases presented a significant overweight of somatic ill health and conflicts in the family. Conclusion: We found a gender difference in the course of bipolar affective disorder, as women had a significantly higher number of depressive episodes than men and men had a higher number of manic episodes than women. In bipolar patients with long duration of disease a significant number of depressive episodes in women were preceded by negative life events. Somatic health problems and conflicts in the family were significant factors preceding new depressive phases.