This survey of 1474 special care units in the United States found that smaller hospitals tended to have only one ICU. The number of ICUs increased with overall hospital size; when a hospital had two ICUs, the second unit was usually for coronary care. Internists directed most of the ICUs, followed in decreasing order by surgeons, family practitioners, anesthesiologists, and pediatricians. More than 40% of ICUs were directed by cardiologists, reflecting the frequency of coronary care units. About eight times as many pulmonary medicine physicians directed ICUs as intensivists trained in critical care medicine. An increasing number of ICU directors received salaries for their services as hospital size increased, and the size of this salary also tended to increase with unit size. Average nurse/patient ratios tended to be better than 1:2.3 for all shifts. Few ICUs used private-duty nurses, although a substantial number required per-diem nurses. The level of nurse education increased with the size of the unit. The number of house officers varied widely according to hospital size, as did the numbers of subspecialty fellows and nonphysician professional and paraprofessional personnel. The availability of services in hospitals also varied according to hospital size, particularly for intra-aortic balloon counterpulsation, CT scanning, and intracranial pressure monitoring. Urban setting more significantly affected size and available services than did geographic region.(ABSTRACT TRUNCATED AT 250 WORDS)