Bipolar disorder not otherwise specified (BPD-NOS) may be a waste-basket diagnosis for patients who do not fit into the well-defined criteria. There are few studies investigating the course and features of BPD-NOS and some authors claimed that the frequency could be higher than expected. Özcan et al (2003) found that 9% of the bipolar patients in a university research clinic specialized in bipolar disorder were diagnosed as BPD-NOS. Frequency of BPD-NOS among bipolar patients hospitalized in year 2006 in a a tertiary care state reference hospital in İstanbul/Turkey and features leading to the diagnosis as “atypical” are investigated.

Files of patients hospitalized in 2006 were evaluated retrospectively. Of the 6423 general psychiatric hospitalizations, 1463 were diagnosed as mood disorders. Forensic and adolescent patients, as well as alcohol & substance abuse co-morbidity were excluded.

There were 821 (56%) male and 642 (44%) female mood disorder patients. BPD-NOS diagnosis among all mood disorder patients were 194 (13.2%). Re-hospitalization rate of patients treated with the diagnosis of BPD-NOS was 6.7%. Duration of illness, episode duration, symptom variety and treatment responses were he most common features “making the diagnosis atypical”.

A more systematic and detailed evaluation is needed for appropriate acute or preventive treatment. Studies are needed on patients with BD-NOS with comorbid schizophrenia or delusional disorder as specified in DSM-IV-TR.