Background: Indigenous primary health-care (PHC) services participating in continuous quality improvement (CQI) cycles show varying patterns of performance over time. Understanding this variation is essential to scaling up and sustaining quality improvement initiatives. The aim of this study is to examine trends in quality of care for services participating in the ABCD National Research Partnership and describe patterns of change over time and examine health service characteristics associated with positive and negative trends in quality of care. setting and participants: PHC services providing care for Indigenous people in urban, rural, and remote northern Australia that had completed at least three annual audits of service delivery for at least one aspect of care (n = 73). Methods/design: Longitudinal clinical audit data from use of four clinical audit tools (maternal health, child health, preventive health, Type 2 diabetes) between 2005 and 2013 were analyzed. Health center performance was classified into six patterns of change over time: consistent high improvement (positive), sustained high performance (positive), decline (negative), marked variability (negative), consistent low performance (negative), and no specific increase or decrease (neutral). Backwards stepwise multiple logistic regression analyses were used to examine the associations between health service characteristics and positive or negative trends in quality of care. results: Trends in quality of care varied widely between health services across the four audit tools. Regression analyses of health service characteristics revealed no consistent statistically significant associations of population size, remoteness, governance model, or accreditation status with positive or negative trends in quality of care. conclusion: The variable trends in quality of care as reflected by CQI audit tools do not appear to be related to easily measurable health service characteristics. This points to the need for a deeper or more nuanced understanding of factors that moderate the effect of CQI on health service performance for the purpose of strengthening enablers and overcoming barriers to improvement.