The complex interrelationship between personality disorders and bipolar disorders is still a controversial aspect with multiple diagnosis, therapeutic and ethiologic implications.

Comorbidity has been defined as the presence of more than one disorder in the same patient at the same time.

We made a literature review between 1995 and 2005 about comorbidity in bipolar and personality disorders.

There are different studies that agree the theory that personality disorders are previous forms of bipolar disorders.

Besides, it is important to consider the effect that bipolar disorders have over personality.

In the last years, different authors have suggested that co-morbid personality disorders predict a worse evolution in the course of the bipolar disorders, finding recurrent and resistant to treatment affective symptoms.

The co-occurrence studies of personality and affective disorders have ranged from 3 to 70%.

If we take the global n (428) of all the reviewed articles, we see that the percentage of comorbidity between personality disorders and bipolar disorders is almost the 48% of the studied patients. Looking at the most prevalent cluster, cluster A is the 13%, cluster B is near the 39% and cluster C the 35%.

Personality traits, dimensions and personality disorders seem to play an important role in the evolution of bipolar disorders.

The identification of these specific personality traits and the knowledge of the influence in the evolution of the illness are extremely important in the treatment and prevention of bipolar disorders.