Background Nurse staffing interventions have been introduced across countries in recent years in response to changing patient requirements, developments in patient care, and shortages of qualified nursing staff. These include changes in skill mix, grade mix or qualification mix, staffing levels, nursing shifts or nurses’ work patterns. Nurse staffing has been closely linked to patient outcomes, organisational outcomes such as costs, and staff-related outcomes. Objectives Our aim was to explore the effect of hospital nurse staffing models on patient and staff-related outcomes. Search methods We searched the following databases from inception through to May 2009: Cochrane/EPOC resources (DARE, CENTRAL, the EPOC Specialised Register), PubMed, EMBASE, CINAHL Plus, CAB Health, Virginia Henderson International Nursing Library, the Joanna Briggs Institute database, the British Library, international theses databases, as well as generic search engines. Selection criteria Randomised control trials, controlled clinical trials, controlled before and after studies and interrupted time series analyses of interventions relating to hospital nurse staffing models. Participants were patients and nursing staff working in hospital settings. We included any objective measure of patient or staff-related outcome. Data collection and analysis Seven reviewers working in pairs independently extracted data from each potentially relevant study and assessed risk of bias. Main results We identified 6,202 studies that were potentially relevant to our review. Following detailed examination of each study, we included 15 studies in the review. Despite the number of studies conducted on this topic, the quality of evidence overall was very limited. We found no evidence that the addition of specialist nurses to nursing staff reduces patient death rates, attendance at the emergency department, or readmission rates, but it is likely to result in shorter patient hospital stays, and reductions in pressure ulcers. The evidence in relation to the impact of replacing Registered Nurses with unqualified nursing assistants on patient outcomes is very limited. However, it is suggested that specialist support staff, such as dietary assistants, may have an important impact on patient outcomes. Self-scheduling and primary nursing may reduce staff turnover. The introduction of team midwifery (versus standard care) may reduce medical procedures in labour and result in a shorter length of stay without compromising maternal or perinatal safety. We found no eligible studies of educational interventions, grade mix interventions, or staffing levels and therefore we are unable to draw conclusions in relation to these interventions. Authors’ conclusions The findings suggest interventions relating to hospital nurse staffing models may improve some patient outcomes, particularly the addition of specialist nursing and specialist support roles to the nursing workforce. Interventions relating to hospital nurse staffing models may also improve staff-related outcomes, particularly the introduction of primary nursing and self scheduling. However, these findings should be treated with extreme caution due to the limited evidence available from the research conducted to date.