This pilot study describes the medical care and demographic characteristics of "difficult" patients as compared with randomly selected patients of a community-based family practice center. Ninety-two difficult patients were identified by asking physicians to indicate those patients whose care they considered difficult. Charts of 166 randomly selected patients were then compared with those of the difficult patients. The difficult patient group was older, more often divorced or widowed, and had a higher percentage of women than the random patient group. The difficult patient group also had more acute problems, chronic problems, medications, x-ray examinations, blood tests, physician referrals, and visits to the family practice center. After covariance analysis adjusting for age and sex, significant differences remained between the two groups for chronic problems, blood tests, medications, and visits to the family practice center. The two patient groups did not differ significantly in household composition, payment status, or provider continuity. The data suggest that, although there are different types of difficult patients, there may be certain medical and demographic features that are common to many of them. Many physicians suspect that difficult patients suffer from a "thick-chart syndrome," a syndrome confirmed to exist by this study.