The direct relationship between registered nurse staffing and the safety of inpatient care is supported by a large body of literature. In addition to staffing ratios, safety culture has also been found to be a determinant of errors. This study explored the links between nurse staffing, safety culture, and medication errors, and found evidence for a complex relationship. The learning climate (a component of safety culture that measures communication between providers) was directly correlated with medication error rate, and also appeared to interact with staffing ratios. Nursing units with a negative learning climate reported more medication errors if they were also staffed by a lower proportion of registered nurses. An Institute of Medicine report called for improving patient safety by addressing cultural factors, including learning climate, that negatively influence nurse working conditions.