Approximately 21% of patients with bipolar disorder (BD) also have an additional diagnosis of obsessive-compulsive disorder (OCD). This condition is associated with a more severe prognosis and complicates the treatment of BD. In our case report we provide documentary evidence of our experience with trazodone prolonged release in the treatment of depressive phase in a patient with BD II-OCD comorbidity. Rationality in the choise of treatment was based on the need to manage depressive and obsessive symptoms without facilitating hypomania switches.