Abstract: A tamper-proof closure cap for use with the externally threaded neck opening of a container for providing a visible indication of tampering attempts with the container includes a generally cylindrical main body portion which is internally threaded and suitable for mating engagement with the externally threaded neck opening. Extending around the lower edge of the main body portion and for approximately 150.degree. is a removable sector ring which is joined to the main body portion by three evenly spaced-apart connecting elements. Located adjacent to the externally threaded neck opening is an interlock protuberance which includes an inclined lower surface and the top surface of the removable sector ring has a compatible sawtooth profile. The teeth of the sawtooth profile ratchetly engage the inclined surface of the interlock protuberance.