BACKGROUND: Development of indicators to measure health-care quality has progressed rapidly. This development has, however, rarely occurred in a systematic fashion, and some aspects of care have received more attention than others. The aim of this study is to identify and classify indicators currently in use to measure the quality of care provided by hospitals, and to identify gaps in current measurement. METHODS: A literature search was undertaken to identify indicator sets. Indicators were included if they related to hospital care and were clearly being collected and reported to an external body. A two-person independent review was undertaken to classify indicators according to aspects of care provision (structure, process or outcome), dimensions of quality (safety, effectiveness, efficiency, timeliness, patient-centredness and equity), and domain of application (hospital-wide, surgical and non-surgical clinical specialities). RESULTS: 383 discrete indicators were identified from 22 source organizations or projects. Of these, 27.2% were relevant hospital-wide, 26.1% to surgical patients and 46.7% to non-surgical specialities, departments or diseases. Cardiothoracic surgery, cardiology and mental health were the specialities with greatest coverage, while nine clinical specialities had fewer than three specific indicators. Processes of care were measured by 54.0% of indicators and outcomes by 38.9%. Safety and effectiveness were the domains most frequently represented, with relatively few indicators measuring the other dimensions. CONCLUSION: Despite the large number of available indicators, significant gaps in measurement still exist. Development of indicators to address these gaps should be a priority. Work is also required to evaluate whether existing indicators measure what they purport to measure.