The factors of age, sex, specialty or primary interest, specialty board status, neighborhood of practice, and medical school are examined in relation to whether or not physicians in private practice in the Southern New York Region have appointments to a hospital medical staff. Evidence is adduced to suggest that the existence of the isolated practitioner is probably a function of several variables. While it appears that the medical staff of many hospitals utilize quite selective criteria pertaining to the admission of new members, it seems likely from the data that the individual physician’s perception of the relevance of a hospital appointment is quite varied, being greatly affected by his personal and professional interests, and that as a consequence his motivation to achieve membership is also varied. The implications of such findings are that community, institutional, and individual responsibility should be exercised toward assuring opportunities for institutional affiliation to all licensed physicians and for motivating physicians to seek such opportunities.