This study determined the effects of nurse staffing and nursing organization on the likelihood of needlestick injuries in hospital nurses. The authors analyzed retrospective data from 732 and prospective data from 960 nurses on needlestick exposures and near misses over different one-month periods in 1990 and 1991. Staffing levels and survey data about working climate and risk factors for needlestick injuries were collected on 40 units in 20 hospitals. Nurses from units with low staffing and poor organizational climates were generally twice as likely as nurses on well-staffed and better-organized units to report risk factors, needlestick injuries, and near misses. Staffing and organizational climate influence hospital nurses' likelihood of sustaining needlestick injuries. Remedying problems with understaffing, inadequate administrative support, and poor morale could reduce needlestick injuries.