The Agency for Healthcare Research and Quality (AHRQ) recommends that hospitals monitor the culture of safety to assess their specific needs for improvement. This study reports on how responses to a nursing survey administered at 13 Catholic health system hospitals were used to develop an instrument that measures safety culture. Higher scores on the resulting instrument, dubbed the Safety Organizing Scale (SOS), were associated with fewer reported medication errors and falls. A prior study evaluated the quality of safety culture measurement instruments and found that most had not been well validated.