Aims and objectives: The study aimed to explore whether nurse staffing, experience and skill mix influenced the model of nursing care in medical-surgical wards. Background: Methods of allocating nurses to patients are typically divided into four types: primary nursing, patient allocation, task assignment and team nursing. Research findings are varied in regard to the relationship between these models of care and outcomes such as satisfaction and quality. Skill mix has been associated with various models, with implications for collegial support, teamwork and patient outcomes. Design: Secondary analysis of data collected on 80 randomly selected medical-surgical wards in 19 public hospitals in New South Wales, Australia during 2004-2005. Methods: Nurses (n = 2278, 80·9% response rate) were surveyed using The Nursing Care Delivery System and the Nursing Work Index-Revised. Staffing and skill mix was obtained from the ward roster and other data from the patient record. Models of care were examined in relation to these practice environment and organisational variables. Results: The models of nursing care most frequently reported by nurses in medical-surgical wards in this study were patient allocation (91%) and team nursing (80%). Primary nursing and task based models were unlikely to be practised. Skill mix, nurse experience, nursing workload and factors in the ward environment significantly influenced the model of care in use. Wards with a higher ratio of degree qualified, experienced registered nurses, working on their 'usual' ward were more likely to practice patient allocation while wards with greater variability in staffing levels and skill mix were more likely to practice team nursing. Conclusions: Models of care are not prescriptive but are varied according to ward circumstances and staffing levels based on complex clinical decision making skills. Relevance to clinical practice: Variability in the models of care reported by ward nurses indicates that nurses adapt the model of nursing care on a daily or shift basis, according to patients' needs, skill mix and individual ward environments.