Does legal defensiveness significantly influence physicians' assessments of medical futility, in ways that may adversely affect the rights of patients and their family members to make their own health care decisions at the end of life? This exploratory study addresses that question with attitudinal data from a survey of 301 physicians practicing in academic medical centers in Texas. The majority of respondents indicated that the probability of success defining futile treatment should hypothetically be lower for patients with potential to benefit more from life-sustaining medical intervention (e.g. typically patients who are sentient), and higher for patients with less potential to benefit (e.g. patients in a persistent vegetative state). That is to say, physicians normally perceive longer odds to be worth pursuing for greater potential gain - a position that seems logically consonant with patients' rational self-interest. However, physicians with an attitude of extreme legal defensiveness did not fit this pattern. Rather, they tended to define futility in a manner that would maximize the physician's latitude to justifiably oppose patient preferences for end-of-life treatment abatement. These findings suggest that some physicians assume an adversarial position in their consideration of medical futility issues - an attitude that anticipates conflict with terminally-ill patients or their surrogates. The analysis presented here is not definitive, but at least raises the question of whether some physicians may inappropriately use their prerogative over medical futility as a means to guard their professional autonomy against perceived threats.