OBJECTIVES: To investigate the incidence of carcinoma in situ (CIS) in Australia and examine implications for its diagnosis and management, as CIS of the urinary bladder is a non-reportable disease in Australia. METHODS: Analysis of annual hospitalisation data using Australian Institute of Health and Welfare (AIHW) datasets showed an increase in CIS from 2001 onwards. To determine whether the increase seen with AIHW data represented a true increase in the rates offices, patient level data was examined using the Centre for Health record linkage (CHeReL) datasets. RESULTS: CHeReL linked data of 13,790 males and 5902 females, calculated the average incidence of CIS to be 20.9 per 100,000 and 6.5 per 100,000 respectively in those aged > 50 years, showing a rapid increase in the rates of CIS from 2001. There was an 11% (P = 0.04) and 14% (P = 0.02) annual increase in incidence of CIS in men and women and these rates increased with age. CONCLUSIONS: National data (AIHW) substantially underestimate the incidence of CIS in the Australian population. Patient level data suggest CIS rates are rapidly increasing in Australia despite high treatment rates. Closer surveillance and awareness of these high rates warrants further study and we recommend that CIS be considered a reportable disease.