A recent study reported an 8% increase in bipolar diagnoses in public and community mental health services in New South Wales from 2003 to 2014, an increase interpreted by the authors as reflecting increasing diagnostic boundaries of bipolar disorder, and bipolar II in particular. If valid, we would expect an increase in hospital admissions for hypomania as well as for mania and so analysed a relevant dataset to test that hypothesis.

Data were examined for 27,255 individuals hospitalised in NSW psychiatric hospitals over a 14-year period (2000–2014) for ICD-10 diagnosed mania or hypomania and with analyses examining rates of hospitalisation/per year for both mania and for hypomania.

While overall admissions for mania and hypomania increased over the study period by 16.4%, admissions for mania increased by 31.0% and admissions for hypomania actually decreased by 32.1%.

The increased rate in admissions of those with a bipolar disorder appears to reflect a trend over more than four decades. The hypothesis that any increase in the diagnostic boundaries of bipolar II disorder would be associated with an increase in hospitalisation rates was rejected, with the converse trend being identified.