H.R.4138: To amend title XVIII of the Social Security Act to impose minimum nurse staffing ratios in Medicare participating hospitals, and for other purposes.

Registered Nurse Safe Staffing Act of 2007 - Amends part D (Miscellaneous) of title XVIII (Medicare) of the Social Security Act (SSA) to: (1) require each participating hospital to adopt and implement a staffing system that ensures a number of registered nurses on each shift and in each unit of the hospital to ensure appropriate staffing levels for patient care; (2) provide for the public reporting of certain staffing information, including a daily posting for each shift in the hospital of the current number of licensed and unlicensed nursing staff directly responsible for patient care; (3) prescribe recordkeeping, data collection, and evaluation requirements for participating hospitals; (4) specify civil monetary penalties for violations of such requirements; and (5) provide whistleblower protections.