In an effort to account for the effects of both physician and patient characteristics in understanding difficult physician-patient relationships, family physician participants in the Michigan Research Network, a practice-based research network in the state of Michigan, were assessed for their perceptions of "difficult" patients. Twenty-two family physicians responded to a mail survey in which they selected from among their respective practices a sample of patients whose care they considered to be particularly difficult. This sampling procedure resulted in a total of 205 difficult patients. Physicians' perceptions of these patients were obtained through ratings of the applicability of 40 behavioral and physical characteristics drawn from the literature. Factor analysis of these data resulted in the identification of two factors underlying physicians' perceptions of difficult patients: medical uncertainty, characterized by particularly vague, difficult to describe, undifferentiated medical problems; and interpersonal difficulty, reflected in a perceived abrasive behavioral style. In addition, physicians self-rated the importance of various motivations for practicing medicine. The top six ranked mean ratings indicate that the primary motivations for practicing medicine were satisfaction derived from solving medical problems and the desire to help people. The interaction of these physician and patient characteristics is offered as a partial explanation for the development of difficult physician-patient relationships.