To investigate trends in health-related quality of life and health service use associated with diabetes and/or major depression in South Australia from 1998 to 2008.

Data analyzed were from 9,059 persons aged ≥15 years who participated in representative surveys of the South Australian population in 1998, 2004 and 2008. Major depression was determined using the mood module of the Primary Care Evaluation of Mental Disorders (PRIME-MD). Diagnosed diabetes and health service use was determined by self-report. Health-related quality of life was assessed using the 36-item Short-Form Health Survey (SF-36) and the 15-item Assessment of Quality of Life (AQoL) instruments. Weighted age-standardized and multiple-adjusted means of dependent measures were computed.

The prevalence of diabetes only, major depression only, and comorbid diabetes and major depression increased by 74%, 36% and 53% from 1998 to 2008. Mean health-related quality of life scores were 9% to 41% lower (worse), and health service use was 49% higher for persons with comorbid diabetes and major depression than for those with diabetes only (all P-values < 0.05), consistently over the 10-year period.

If past trends continue, our results suggest that the population health and economic burden of comorbid diabetes and major depression will grow similarly over the next decade or so. These trends have important implications for making health policy and resource allocation decisions.