Installation of the first United States 201-source 60Co gamma unit for stereotactic radiosurgery was completed at the University of Pittsburgh in May, 1987. Despite a very favorable 19-year experience in Stockholm, introduction of this technology into the US proved to be a formidable task. Extensive internal and government regulatory review by the Health Systems Agency, the Food and Drug Administration and the Nuclear Regulatory Commission ultimately resulted in approval of marketing and use of the gamma unit. Clinical use and radiobiological research has begun.